drbd: Avoid Clang warning about pointless switch statment

There are several warnings from Clang about no case statement matching
the constant 0:

In file included from drivers/block/drbd/drbd_receiver.c:48:
In file included from drivers/block/drbd/drbd_int.h:48:
In file included from ./include/linux/drbd_genl_api.h:54:
In file included from ./include/linux/genl_magic_struct.h:236:
./include/linux/drbd_genl.h:321:1: warning: no case matching constant
switch condition '0'
GENL_struct(DRBD_NLA_HELPER, 24, drbd_helper_info,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/genl_magic_struct.h:220:10: note: expanded from macro
'GENL_struct'
        switch (0) {
                ^

Silence this warning by adding a 'case 0:' statement. Additionally,
adjust the alignment of the statements in the ct_assert_unique macro to
avoid a checkpatch warning.

This solution was originally sent by Arnd Bergmann with a default case
statement: https://lore.kernel.org/patchwork/patch/756723/

Link: https://github.com/ClangBuiltLinux/linux/issues/43Suggested-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/genl_magic_struct.h

@@ -191,6 +191,7 @@ static inline void ct_assert_unique_operations(void)
 {
 	switch (0) {
 #include GENL_MAGIC_INCLUDE_FILE
+	case 0:
 		;
 	}
 }
@@ -209,6 +210,7 @@ static inline void ct_assert_unique_top_level_attributes(void)
 {
 	switch (0) {
 #include GENL_MAGIC_INCLUDE_FILE
+	case 0:
 		;
 	}
 }
@@ -219,6 +221,7 @@ static inline void ct_assert_unique_ ## s_name ## _attributes(void)	\
 {									\
 	switch (0) {							\
 	s_fields							\
+	case 0:								\
 			;						\
 	}								\
 }