reiserfs: Convert release_buffer_page() to use a folio

Saves 671 bytes from an allmodconfig build (!)

Function                                     old     new   delta
release_buffer_page                         1617     946    -671
Total: Before=67656, After=66985, chg -0.99%

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>