scsi: sg: fix minor memory leak in error path

BugLink: https://bugs.launchpad.net/bugs/1791953

commit c170e5a8 upstream.

Fix a minor memory leak when there is an error opening a /dev/sg device.

Fixes: cc833acb ("sg: O_EXCL and other lock handling")
Cc: <stable@vger.kernel.org>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/scsi/sg.c

@@ -2195,6 +2195,7 @@ sg_add_sfp(Sg_device * sdp)
 	write_lock_irqsave(&sdp->sfd_lock, iflags);
 	if (atomic_read(&sdp->detaching)) {
 		write_unlock_irqrestore(&sdp->sfd_lock, iflags);
+		kfree(sfp);
 		return ERR_PTR(-ENODEV);
 	}
 	list_add_tail(&sfp->sfd_siblings, &sdp->sfds);