block: remove redundant =y from BLK_CGROUP dependency

CONFIG_BLK_CGROUP is a boolean option, that is, its value is 'y' or 'n'.
The comparison to 'y' is redundant.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210927140000.866249-2-masahiroy@kernel.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>