f2fs: remove unneeded check for error allocating bio_post_read_ctx

Since allocating an object from a mempool never fails when
__GFP_DIRECT_RECLAIM (which is included in GFP_NOFS) is set, the check
for failure to allocate a bio_post_read_ctx is unnecessary.  Remove it.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -937,11 +937,8 @@ static struct bio *f2fs_grab_read_bio(struct inode *inode, block_t blkaddr,
 		post_read_steps |= 1 << STEP_VERITY;
 
 	if (post_read_steps) {
+		/* Due to the mempool, this never fails. */
 		ctx = mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
-		if (!ctx) {
-			bio_put(bio);
-			return ERR_PTR(-ENOMEM);
-		}
 		ctx->bio = bio;
 		ctx->sbi = sbi;
 		ctx->enabled_steps = post_read_steps;