PM: hibernate: use correct mode for swsusp_close()

Commit 39fbef4b ("PM: hibernate: Get block device exclusively in
swsusp_check()") changed the opening mode of the block device to
(FMODE_READ | FMODE_EXCL).

In the corresponding calls to swsusp_close(), the mode is still just
FMODE_READ which triggers the warning in blkdev_flush_mapping() on
resume from hibernate.

So, use the mode (FMODE_READ | FMODE_EXCL) also when closing the
device.

Fixes: 39fbef4b ("PM: hibernate: Get block device exclusively in swsusp_check()")
Signed-off-by: Thomas Zeitlhofer <thomas.zeitlhofer+lkml@ze-it.at>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>