The addition of multiple-device support broke CONFIG_BLK_DEV_ZONED
on 32-bit machines because of a 64-bit division:

fs/f2fs/f2fs.o: In function `__issue_discard_async':
extent_cache.c:(.text.__issue_discard_async+0xd4): undefined reference to `__aeabi_uldivmod'

Fortunately, bdev_zone_size() is guaranteed to return a power-of-two
number, so we can replace the % operator with a cheaper bit mask.

Fixes: 792b84b74b54 ("f2fs: support multiple devices")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>