tests: Remove last GLfloat use

With the EGL/GLES2 types out of compositor.h this now fails to compile.

https://bugs.freedesktop.org/show_bug.cgi?id=57129
diff --git a/tests/surface-global-test.c b/tests/surface-global-test.c
index 9923c3d..6e991ba 100644
--- a/tests/surface-global-test.c
+++ b/tests/surface-global-test.c
@@ -27,7 +27,7 @@
 TEST(surface_to_from_global)
 {
 	struct weston_surface *surface;
-	GLfloat x, y;
+	float x, y;
 	wl_fixed_t fx, fy;
 	int32_t ix, iy;