cachefiles: Drop superfluous readpages aops NULL check

After the recent actions to convert readpages aops to readahead, the
NULL checks of readpages aops in cachefiles_read_or_alloc_page() may
hit falsely.  More badly, it's an ASSERT() call, and this panics.

Drop the superfluous NULL checks for fixing this regression.

[DH: Note that cachefiles never actually used readpages, so this check was
 never actually necessary]

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=208883
BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1175245
Fixes: 9ae326a ("CacheFiles: A cache that backs onto a mounted filesystem")
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/cachefiles/rdwr.c

@@ -413,7 +413,6 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
 
 	inode = d_backing_inode(object->backer);
 	ASSERT(S_ISREG(inode->i_mode));
-	ASSERT(inode->i_mapping->a_ops->readpages);
 
 	/* calculate the shift required to use bmap */
 	shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
@@ -713,7 +712,6 @@ int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
 
 	inode = d_backing_inode(object->backer);
 	ASSERT(S_ISREG(inode->i_mode));
-	ASSERT(inode->i_mapping->a_ops->readpages);
 
 	/* calculate the shift required to use bmap */
 	shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;