grub.cfg: also unroll the list of usb devices

resources/grub/config/grub.cfg

@@ -117,7 +117,7 @@ menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o
 #TODO: Pick better variable name scheme than ${ddev}, or find way to make it local
 	unset ahcidev
 	unset atadev
-    unset usbdev
+	unset usbdev
 	if [ (ahci?) != "(ahci?)" ]; then
 		ahcilist=(ahci*)
 		for part in ${ahcilist}; do
@@ -131,7 +131,10 @@ menuentry 'Load Operating System (incl. fully encrypted disks)  [o]' --hotkey='o
 		done
 	fi
 	if [ (usb?) != "(usb?)" ]; then
-		usbdev=(usb*)
+		usblist=(usb*)
+		for part in ${usblist}; do
+	        	usbdev="$part $usbdev"
+		done
 	fi
 	set pager=0
 	echo -n "Attempting to cryptomount: "