cmd_usage(): simplify return code handling

Lots of code use this construct:

	cmd_usage(cmdtp);
	return 1;

Change cmd_usage() let it return 1 - then we can replace all these
ocurrances by

	return cmd_usage(cmdtp);

This fixes a few places with incorrect return code handling, too.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/cmd_log.c b/common/cmd_log.c
index 49deddd..0e89357 100644
--- a/common/cmd_log.c
+++ b/common/cmd_log.c
@@ -241,12 +241,10 @@
 			}
 			return 0;
 		}
-		cmd_usage(cmdtp);
-		return 1;
+		return cmd_usage(cmdtp);
 
 	default:
-		cmd_usage(cmdtp);
-		return 1;
+		return cmd_usage(cmdtp);
 	}
 }