usb: gadget: workaround storage command size issues

Try to workaround issues with bad SCSI implementations
by ignoring the command size error.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>