drm/i915: Fix scaling check for 90/270 degree plane rotation

Starting from commit b63a16f6 ("drm/i915: Compute display surface
offset in the plane check hook for SKL+") we've already rotated the src
coordinates by 270 degrees by the time we check if a scaler is needed
or not, so we must not account for the rotation a second time.
Previously we did these steps in the opposite order and hence the
scaler check had to deal with rotation itself. The double rotation
handling causes us to enable a scaler pretty much every time 90/270
degree plane rotation is requested, leading to fuzzier fonts and whatnot.

v2: s/unsigned/unsigned int/ to appease checkpatch
v3: s/DRM_ROTATE_0/DRM_MODE_ROTATE_0/

Cc: stable@vger.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: b63a16f6 ("drm/i915: Compute display surface offset in the plane check hook for SKL+")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170331180056.14086-2-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>