USBSTOR driver. Handling of result in function USBSTOR_GetMaxLUN()

"USB Mass Storage Class. Bulk-Only Transport. Revision 1.0"
3.2 Get Max LUN (class-specific request) :
Devices that do not support multiple LUNs may STALL this command.

If Usb device not support Get Max LUN then Status may be not success.
As a result - part of Usb devices is not recognized.

The patch resolves this problem.