fscrypt: convert bh_get_inode_and_lblk_num to use a folio

fscrypt: convert bh_get_inode_and_lblk_num to use a folio

Patch series "Remove page_mapping()".

There are only a few users left.  Convert them all to either call
folio_mapping() or just use folio->mapping directly.

This patch (of 6):

Remove uses of page->index, page_mapping() and b_page.  Saves a call
to compound_head().

Link: https://lkml.kernel.org/r/20240423225552.4113447-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20240423225552.4113447-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>