scsi: sg: init open_rel_lock mutex

Commit eeacb548aad15f900edffa6218c7e0e749eac8c3 left it uninitialized.

Change-Id: I931158cb0d766350be26ad82cd98d0010113d895
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
1 file changed