drm/msm/dpu: Add check for pstates

As kzalloc may fail and return NULL pointer,
it should be better to check pstates
in order to avoid the NULL pointer dereference.

Fixes: 25fdd593 ("drm/msm: Add SDM845 DPU support")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/514160/
Link: https://lore.kernel.org/r/20221206080236.43687-1-jiasheng@iscas.ac.cnSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c

@@ -1153,6 +1153,8 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 	bool needs_dirtyfb = dpu_crtc_needs_dirtyfb(crtc_state);
 
 	pstates = kzalloc(sizeof(*pstates) * DPU_STAGE_MAX * 4, GFP_KERNEL);
+	if (!pstates)
+		return -ENOMEM;
 
 	if (!crtc_state->enable || !crtc_state->active) {
 		DRM_DEBUG_ATOMIC("crtc%d -> enable %d, active %d, skip atomic_check\n",