logging_vty.c: Avoid acquiring log tgt lock in logging level cmd when not needed

Change-Id: Ia6780221174070cee408625e24513f2c11cc9dfc
diff --git a/src/vty/logging_vty.c b/src/vty/logging_vty.c
index 6d908d9..c51b437 100644
--- a/src/vty/logging_vty.c
+++ b/src/vty/logging_vty.c
@@ -351,18 +351,18 @@
 	int category = log_parse_category(argv[0]);
 	int level = log_parse_level(argv[1]);
 
-	ACQUIRE_VTY_LOG_TGT_WITH_LOCK(vty, tgt);
-
 	if (level < 0) {
 		vty_out(vty, "Invalid level `%s'%s", argv[1], VTY_NEWLINE);
-		RET_WITH_UNLOCK(CMD_WARNING);
+		return CMD_WARNING;
 	}
 
 	if (category < 0) {
 		vty_out(vty, "Invalid category `%s'%s", argv[0], VTY_NEWLINE);
-		RET_WITH_UNLOCK(CMD_WARNING);
+		return CMD_WARNING;
 	}
 
+	ACQUIRE_VTY_LOG_TGT_WITH_LOCK(vty, tgt);
+
 	tgt->categories[category].enabled = 1;
 	tgt->categories[category].loglevel = level;