egl/x11: Remove unneeded free() on always null string

In this condition dri2_dpy->driver_name string always equals
NULL, so call to free() is useless

Signed-off-by: Vadym Shovkoplias <vadym.shovkoplias@globallogic.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

src/egl/drivers/dri2/platform_x11.c

@@ -704,7 +704,6 @@ dri2_x11_connect(struct dri2_egl_display *dri2_dpy)
 
    if (dri2_dpy->driver_name == NULL) {
       close(dri2_dpy->fd);
-      free(dri2_dpy->driver_name);
       free(connect);
       return EGL_FALSE;
    }