ceph: Convert ceph_find_incompatible() to take a folio

ceph: Convert ceph_find_incompatible() to take a folio

Both callers already have the folio.  Pass it in and use it throughout.
Removes some hidden calls to compound_head() and a reference to
page->mapping.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250217185119.430193-4-willy@infradead.org
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>