drm/i915: Drop I915_ prefix from HAS_FBC

My OCD just couldn't let this slide. Spotted while reviewing Ville's
patch to only flip planes when we have FBC.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 158cb30..261254a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3220,7 +3220,7 @@
 
 		for_each_pipe(pipe) {
 			int plane = pipe;
-			if (I915_HAS_FBC(dev))
+			if (HAS_FBC(dev))
 				plane = !plane;
 
 			if (pipe_stats[pipe] & PIPE_VBLANK_INTERRUPT_STATUS &&
@@ -3421,7 +3421,7 @@
 
 		for_each_pipe(pipe) {
 			int plane = pipe;
-			if (I915_HAS_FBC(dev))
+			if (HAS_FBC(dev))
 				plane = !plane;
 
 			if (pipe_stats[pipe] & PIPE_VBLANK_INTERRUPT_STATUS &&