logging: Add missing va_end in log_msg2

Added missing va_end. Reported by coverity CID 232501

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
diff --git a/subsys/logging/log_msg2.c b/subsys/logging/log_msg2.c
index ad80d98..b13a7d3 100644
--- a/subsys/logging/log_msg2.c
+++ b/subsys/logging/log_msg2.c
@@ -58,13 +58,15 @@
 				const char *fmt, va_list ap)
 {
 	int plen;
-	va_list ap2;
 
 	if (fmt) {
+		va_list ap2;
+
 		va_copy(ap2, ap);
 		plen = cbvprintf_package(NULL, Z_LOG_MSG2_ALIGN_OFFSET,
 					 fmt, ap2);
 		__ASSERT_NO_MSG(plen >= 0);
+		va_end(ap2);
 	} else {
 		plen = 0;
 	}