swsusp: don't pass a stack address to blkdev_get_by_path

holder is just an on-stack pointer that can easily be reused by other calls,
replace it with a static variable that doesn't change.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230608110258.189493-12-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

kernel/power/swap.c

@@ -1510,6 +1510,8 @@ int swsusp_read(unsigned int *flags_p)
 	return error;
 }
 
+static void *swsusp_holder;
+
 /**
  *      swsusp_check - Check for swsusp signature in the resume device
  */
@@ -1517,14 +1519,13 @@ int swsusp_read(unsigned int *flags_p)
 int swsusp_check(bool snapshot_test)
 {
 	int error;
-	void *holder;
 	fmode_t mode = FMODE_READ;
 
 	if (snapshot_test)
 		mode |= FMODE_EXCL;
 
 	hib_resume_bdev = blkdev_get_by_dev(swsusp_resume_device,
-					    mode, &holder, NULL);
+					    mode, &swsusp_holder, NULL);
 	if (!IS_ERR(hib_resume_bdev)) {
 		set_blocksize(hib_resume_bdev, PAGE_SIZE);
 		clear_page(swsusp_header);