USB: storage: avoid scanning other targets for single target device

This patch sets scsi_host->max_id as 1 if the device's quirk
flag of US_FL_SCM_MULT_TARG isn't set, because there are only 6
mass storage devices marked as mutiple targets from unusual_devs.h.

This patch is a small optimization about scanning targets, and
avoid scanning other 7 non-existed targets for single target
device.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Acked-by: NMatthew Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/storage/usb.c

@@ -976,6 +976,9 @@ int usb_stor_probe2(struct us_data *us)
 	if (us->fflags & US_FL_SINGLE_LUN)
 		us->max_lun = 0;
 
+	if (!(us->fflags & US_FL_SCM_MULT_TARG))
+		us_to_host(us)->max_id = 1;
+
 	/* Find the endpoints and calculate pipe values */
 	result = get_pipes(us);
 	if (result)