blockdev: convert some macros to static inlines

We prefer to program in C rather than preprocessor and it fixes this
warning when CONFIG_BLK_DEV_INTEGRITY is not set:

drivers/md/dm-table.c: In function 'dm_table_set_integrity':
drivers/md/dm-table.c:1285:3: warning: statement with no effect [-Wunused-value]

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>