tests: Fix build with clang

clang doesn't like mode_t type as an argument to va_arg():

error: second argument to 'va_arg' is of promotable type 'mode_t' (aka
'unsigned short'); this va_arg has undefined behavior because arguments
will be promoted to 'int'

    mode = va_arg(ap, mode_t);
                      ^~~~~~
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

tests/virfilewrapper.c

@@ -267,7 +267,7 @@ int open(const char *path, int flags, ...)
      */
     if (flags & O_CREAT) {
         va_start(ap, flags);
-        mode = va_arg(ap, mode_t);
+        mode = (mode_t) va_arg(ap, int);
         va_end(ap);
     }
 

tests/virusbmock.c

@@ -101,7 +101,7 @@ int open(const char *pathname, int flags, ...)
      */
     if (flags & O_CREAT) {
         va_start(ap, flags);
-        mode = va_arg(ap, mode_t);
+        mode = (mode_t) va_arg(ap, int);
         va_end(ap);
     }