drm/i915: Use pixel size for computing linear offsets into a sprite

This fixes an original bug in the sprite code that miscomputed the
source offset into a linear YUV packed framebuffer, that was magnified
into an oops with

commit 5a35e99e8162d6820013a56ad15ea8bf937af5a6
Author: Damien Lespiau <damien.lespiau@intel.com>
Date:   Fri Oct 26 18:20:12 2012 +0100

    drm/i915: adjust sprite base address

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.com>
Cc: Damien Lespiau <damien.lespiau@intel.com>
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>

drivers/gpu/drm/i915/intel_sprite.c

@@ -120,11 +120,10 @@ ivb_update_plane(struct drm_plane *plane, struct drm_framebuffer *fb,
 	I915_WRITE(SPRSTRIDE(pipe), fb->pitches[0]);
 	I915_WRITE(SPRPOS(pipe), (crtc_y << 16) | crtc_x);
 
-	linear_offset = y * fb->pitches[0] + x * (fb->bits_per_pixel / 8);
+	linear_offset = y * fb->pitches[0] + x * pixel_size;
 	sprsurf_offset =
 		intel_gen4_compute_offset_xtiled(&x, &y,
-						 fb->bits_per_pixel / 8,
-						 fb->pitches[0]);
+						 pixel_size, fb->pitches[0]);
 	linear_offset -= sprsurf_offset;
 
 	/* HSW consolidates SPRTILEOFF and SPRLINOFF into a single SPROFFSET
@@ -286,11 +285,10 @@ ilk_update_plane(struct drm_plane *plane, struct drm_framebuffer *fb,
 	I915_WRITE(DVSSTRIDE(pipe), fb->pitches[0]);
 	I915_WRITE(DVSPOS(pipe), (crtc_y << 16) | crtc_x);
 
-	linear_offset = y * fb->pitches[0] + x * (fb->bits_per_pixel / 8);
+	linear_offset = y * fb->pitches[0] + x * pixel_size;
 	dvssurf_offset =
 		intel_gen4_compute_offset_xtiled(&x, &y,
-						 fb->bits_per_pixel / 8,
-						 fb->pitches[0]);
+						 pixel_size, fb->pitches[0]);
 	linear_offset -= dvssurf_offset;
 
 	if (obj->tiling_mode != I915_TILING_NONE)