usb: f_mass_storage: set removable flag in do_inquiry based on LUN

Without this flag, tools like Alex Page's USB Image Tool
won't see drives exposed over USB Gadget as removable,
and won't allow access to them.
	http://www.alexpage.de/usb-image-tool/

The code was pulled from the main-line kernel:
	drivers/usb/gadget/function/f_mass_storage.c

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>

drivers/usb/gadget/f_mass_storage.c

@@ -1110,6 +1110,7 @@ static int do_inquiry(struct fsg_common *common, struct fsg_buffhd *bh)
 
 	memset(buf, 0, 8);
 	buf[0] = TYPE_DISK;
+	buf[1] = curlun->removable ? 0x80 : 0;
 	buf[2] = 2;		/* ANSI SCSI level 2 */
 	buf[3] = 2;		/* SCSI-2 INQUIRY data format */
 	buf[4] = 31;		/* Additional length */