dmesg: fix possible memory leak [coverity scan]

Signed-off-by: Karel Zak <kzak@redhat.com>

sys-utils/dmesg.c

@@ -1085,10 +1085,10 @@ full_output:
 			mesg_size = strlen(line);
 			goto full_output;
 		}
-		free(mesg_copy);
 	}
 
 done:
+	free(mesg_copy);
 	putchar('\n');
 }