f2fs: remove unnecessary block size check in init_f2fs_fs()

After commit d7e9a903

 ("f2fs: Support Block Size == Page Size"),
F2FS_BLKSIZE equals to PAGE_SIZE, remove unnecessary check condition.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>