drm/i915: Fix 90/270 rotated coordinates for FBC

The clipped src coordinates have already been rotated by 270 degrees for
when the plane rotation is 90/270 degrees, hence the FBC code should no
longer swap the width and height.

Cc: stable@vger.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@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/20170331180056.14086-4-ville.syrjala@linux.intel.com
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
(cherry picked from commit 73714c05

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>