drm: Add "prefix" parameter to drm_rect_debug_print()

Allow the caller to specify a "prefix" string to drm_rect_debug_print()
to make it easier to see which drm_rect is being printed.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index 56dc132..c3b7359 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -832,8 +832,8 @@
 		hscale = drm_rect_calc_hscale(src, dst, min_scale, max_scale);
 		if (hscale < 0) {
 			DRM_DEBUG_KMS("Horizontal scaling factor out of limits\n");
-			drm_rect_debug_print(src, true);
-			drm_rect_debug_print(dst, false);
+			drm_rect_debug_print("src: ", src, true);
+			drm_rect_debug_print("dst: ", dst, false);
 
 			return hscale;
 		}
@@ -841,8 +841,8 @@
 		vscale = drm_rect_calc_vscale(src, dst, min_scale, max_scale);
 		if (vscale < 0) {
 			DRM_DEBUG_KMS("Vertical scaling factor out of limits\n");
-			drm_rect_debug_print(src, true);
-			drm_rect_debug_print(dst, false);
+			drm_rect_debug_print("src: ", src, true);
+			drm_rect_debug_print("dst: ", dst, false);
 
 			return vscale;
 		}