drm: Fix drm_fixp2int_round() making it add 0.5

As well noted by Pekka[1], the rounding of drm_fixp2int_round is wrong.
To round a number, you need to add 0.5 to the number and floor that,
drm_fixp2int_round() is adding 0.0000076. Make it add 0.5.

[1]: https://lore.kernel.org/all/[email protected]/

Fixes: 8b25320 ("drm: Add fixed-point helper to get rounded integer values")
Suggested-by: Pekka Paalanen <[email protected]>
Reviewed-by: Harry Wentland <[email protected]>
Reviewed-by: Melissa Wen <[email protected]>
Signed-off-by: Arthur Grillo <[email protected]>
Signed-off-by: Melissa Wen <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Grillo-0

include/drm/drm_fixed.h

@@ -71,7 +71,6 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
 }
 
 #define DRM_FIXED_POINT		32
-#define DRM_FIXED_POINT_HALF	16
 #define DRM_FIXED_ONE		(1ULL << DRM_FIXED_POINT)
 #define DRM_FIXED_DECIMAL_MASK	(DRM_FIXED_ONE - 1)
 #define DRM_FIXED_DIGITS_MASK	(~DRM_FIXED_DECIMAL_MASK)
@@ -90,7 +89,7 @@ static inline int drm_fixp2int(s64 a)
 
 static inline int drm_fixp2int_round(s64 a)
 {
-	return drm_fixp2int(a + (1 << (DRM_FIXED_POINT_HALF - 1)));
+	return drm_fixp2int(a + DRM_FIXED_ONE / 2);
 }
 
 static inline int drm_fixp2int_ceil(s64 a)