drm: Don't treat 0 as -1 in drm_fixp2int_ceil

Unit testing this in VKMS shows that passing 0 into
this function returns -1, which is highly counter-
intuitive. Fix it by checking whether the input is
>= 0 instead of > 0.

Fixes: 64566b5e ("drm: Add drm_fixp_from_fraction and drm_fixp2int_ceil")
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231108163647.106853-2-harry.wentland@amd.com

include/drm/drm_fixed.h

@@ -95,7 +95,7 @@ static inline int drm_fixp2int_round(s64 a)
 
 static inline int drm_fixp2int_ceil(s64 a)
 {
-	if (a > 0)
+	if (a >= 0)
 		return drm_fixp2int(a + DRM_FIXED_ALMOST_ONE);
 	else
 		return drm_fixp2int(a - DRM_FIXED_ALMOST_ONE);