cmd_usb.c: print debug messages only when DEBUG is defined

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/cmd_usb.c b/common/cmd_usb.c
index 9de515c..6b5c582 100644
--- a/common/cmd_usb.c
+++ b/common/cmd_usb.c
@@ -601,7 +601,7 @@
 					ok++;
 					if (devno)
 						printf("\n");
-					printf("print_part of %x\n", devno);
+					debug("print_part of %x\n", devno);
 					print_part(stor_dev);
 				}
 			}
@@ -610,7 +610,7 @@
 			stor_dev = usb_stor_get_dev(devno);
 			if (stor_dev->type != DEV_TYPE_UNKNOWN) {
 				ok++;
-				printf("print_part of %x\n", devno);
+				debug("print_part of %x\n", devno);
 				print_part(stor_dev);
 			}
 		}