ceph: Use a folio in ceph_page_mkwrite()

ceph: Use a folio in ceph_page_mkwrite()

Convert the passed page to a folio and use it
throughout ceph_page_mkwrite().  Removes the last call to
page_mkwrite_check_truncate(), the last call to offset_in_thp() and one
of the last calls to thp_size().  Saves a few calls to compound_head().

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250217185119.430193-3-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>