Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: arm):

drivers/crypto/ux500/cryp/cryp.c: In function ‘cryp_save_device_context’:
drivers/crypto/ux500/cryp/cryp.c:316:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
   ctx->key_4_r = readl_relaxed(&src_reg->key_4_r);
drivers/crypto/ux500/cryp/cryp.c:318:2: note: here
  case CRYP_KEY_SIZE_192:
  ^~~~
drivers/crypto/ux500/cryp/cryp.c:320:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
   ctx->key_3_r = readl_relaxed(&src_reg->key_3_r);
drivers/crypto/ux500/cryp/cryp.c:322:2: note: here
  case CRYP_KEY_SIZE_128:
  ^~~~
drivers/crypto/ux500/cryp/cryp.c:324:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
   ctx->key_2_r = readl_relaxed(&src_reg->key_2_r);
drivers/crypto/ux500/cryp/cryp.c:326:2: note: here
  default:
  ^~~~~~~
In file included from ./include/linux/io.h:13:0,
                 from drivers/crypto/ux500/cryp/cryp_p.h:14,
                 from drivers/crypto/ux500/cryp/cryp.c:15:
drivers/crypto/ux500/cryp/cryp.c: In function ‘cryp_restore_device_context’:
./arch/arm/include/asm/io.h:92:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
 #define __raw_writel __raw_writel
                      ^
./arch/arm/include/asm/io.h:299:29: note: in expansion of macro ‘__raw_writel’
 #define writel_relaxed(v,c) __raw_writel((__force u32) cpu_to_le32(v),c)
                             ^~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:363:3: note: in expansion of macro ‘writel_relaxed’
   writel_relaxed(ctx->key_4_r, &reg->key_4_r);
   ^~~~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:365:2: note: here
  case CRYP_KEY_SIZE_192:
  ^~~~
In file included from ./include/linux/io.h:13:0,
                 from drivers/crypto/ux500/cryp/cryp_p.h:14,
                 from drivers/crypto/ux500/cryp/cryp.c:15:
./arch/arm/include/asm/io.h:92:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
 #define __raw_writel __raw_writel
                      ^
./arch/arm/include/asm/io.h:299:29: note: in expansion of macro ‘__raw_writel’
 #define writel_relaxed(v,c) __raw_writel((__force u32) cpu_to_le32(v),c)
                             ^~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:367:3: note: in expansion of macro ‘writel_relaxed’
   writel_relaxed(ctx->key_3_r, &reg->key_3_r);
   ^~~~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:369:2: note: here
  case CRYP_KEY_SIZE_128:
  ^~~~
In file included from ./include/linux/io.h:13:0,
                 from drivers/crypto/ux500/cryp/cryp_p.h:14,
                 from drivers/crypto/ux500/cryp/cryp.c:15:
./arch/arm/include/asm/io.h:92:22: warning: this statement may fall through [-Wimplicit-fallthrough=]
 #define __raw_writel __raw_writel
                      ^
./arch/arm/include/asm/io.h:299:29: note: in expansion of macro ‘__raw_writel’
 #define writel_relaxed(v,c) __raw_writel((__force u32) cpu_to_le32(v),c)
                             ^~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:371:3: note: in expansion of macro ‘writel_relaxed’
   writel_relaxed(ctx->key_2_r, &reg->key_2_r);
   ^~~~~~~~~~~~~~
drivers/crypto/ux500/cryp/cryp.c:373:2: note: here
  default:
  ^~~~~~~
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>