Fix the following fallthrough warning:

drivers/pcmcia/db1xxx_ss.c:359:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
           case 3:
           ^
   drivers/pcmcia/db1xxx_ss.c:359:2: note: insert 'break;' to avoid fall-through
           case 3:
           ^
           break;

This helps with the ongoing efforts to globally enable
-Wimplicit-fallthrough for Clang.

Link: https://github.com/KSPP/linux/issues/115
Link: https://lore.kernel.org/linux-mm/202109030839.t2llsvmc-lkp@intel.com/Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>