egl: fix var type

queryImage() takes an `int*`; compiler is warning about the
signed<->unsigned pointer mismatch.

Fixes: 0db36caa19 "egl/wayland: Add a fallback when fourcc
       query isn't supported"
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>

src/egl/drivers/dri2/platform_wayland.c

@@ -676,7 +676,7 @@ get_fourcc(struct dri2_egl_display *dri2_dpy,
            __DRIimage *image, int *fourcc)
 {
    EGLBoolean query;
-   uint32_t dri_format;
+   int dri_format;
 
    query = dri2_dpy->image->queryImage(image, __DRI_IMAGE_ATTRIB_FOURCC,
                                        fourcc);