drm/i915: Remove redundant check for negative timeout while doing an atomic pipe update

No functional changes, just a minor knit. Stumbled across the kernel doc for
schedule_timeout() which quotes "In all cases the return value is guaranteed
to be non-negative". Also, the return code of schedule_timeout() already checks
for negative values "return timeout < 0 ? 0 : timeout;" and returns 0
in such cases. Furthermore, the msec_to_jiffies returns an ungined long
value. So, let's do away with the redundant check for an atomic
pipe update.

v2: Commit message changes (Manasi).
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502233300.81220-1-tarun.vyas@intel.com

drivers/gpu/drm/i915/intel_sprite.c

@@ -131,7 +131,7 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 		if (scanline < min || scanline > max)
 			break;
 
-		if (timeout <= 0) {
+		if (!timeout) {
 			DRM_ERROR("Potential atomic update failure on pipe %c\n",
 				  pipe_name(crtc->pipe));
 			break;