staging: zcache: fix cleancache crash

After commit c5f5c4db3938 ("staging: zcache: fix crash on high memory
swap") cleancache crashes on the first successful get.  This was caused
by a remaining virt_to_page() call in zcache_pampd_get_data_and_free()
that only gets run in the cleancache path.

The patch converts the virt_to_page() to struct page casting like was
done for other instances in c5f5c4db3938.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Tested-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/staging/zcache/zcache-main.c

@@ -1242,7 +1242,7 @@ static int zcache_pampd_get_data_and_free(char *data, size_t *bufsize, bool raw,
 	int ret = 0;
 
 	BUG_ON(!is_ephemeral(pool));
-	zbud_decompress(virt_to_page(data), pampd);
+	zbud_decompress((struct page *)(data), pampd);
 	zbud_free_and_delist((struct zbud_hdr *)pampd);
 	atomic_dec(&zcache_curr_eph_pampd_count);
 	return ret;