drm: fix lut value extraction function

When extracting the value at full precision (16 bits), no need to
round the value.

This was spotted by Jani when running sparse. Unfortunately this fix
doesn't get rid of the warning.
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reported-by: Jani Nikula <jani.nikula@intel.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: dri-devel@lists.freedesktop.org
Fixes: 5488dc16 ("drm: introduce pipe color correction properties")
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1458655833-19547-1-git-send-email-lionel.g.landwerlin@intel.com

include/drm/drm_crtc.h

@@ -2592,10 +2592,14 @@ static inline struct drm_property *drm_property_find(struct drm_device *dev,
 static inline uint32_t drm_color_lut_extract(uint32_t user_input,
 					     uint32_t bit_precision)
 {
-	uint32_t val = user_input + (1 << (16 - bit_precision - 1));
+	uint32_t val = user_input;
 	uint32_t max = 0xffff >> (16 - bit_precision);
 
-	val >>= 16 - bit_precision;
+	/* Round only if we're not using full precision. */
+	if (bit_precision < 16) {
+		val += 1UL << (16 - bit_precision - 1);
+		val >>= 16 - bit_precision;
+	}
 
 	return clamp_val(val, 0, max);
 }