mufs: fix Valgrind warnings in mufs_abspath() by using calloc() instead of malloc()

source/fs/mufs/dir.c

@@ -17,7 +17,10 @@ char *mufs_abspath(const char *path)
 {
 	char *s, *p, *next, *prev;
 
-	if (!(s = malloc(strlen(path) + 2)))
+	if (!path)
+		return "/";
+
+	if (!(s = calloc(strlen(path) + 2, sizeof *s)))
 		return NULL;
 
 	strcpy(s, path);