drm/msm/dpu: clean up dpu_kms_get_clk_rate() returns

Static analysis tools complain about the -EINVAL error code being
stored in an unsigned variable.  Let's change this to match
the clk_get_rate() function which is type unsigned long and returns
zero on error.

Fixes: 25fdd593 ("drm/msm: Add SDM845 DPU support")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/539626/
Link: https://lore.kernel.org/r/28644c5e-950e-41cd-8389-67f37b067bdc@kili.mountainSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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

@@ -1023,13 +1023,13 @@ static int _dpu_kms_mmu_init(struct dpu_kms *dpu_kms)
 	return 0;
 }
 
-u64 dpu_kms_get_clk_rate(struct dpu_kms *dpu_kms, char *clock_name)
+unsigned long dpu_kms_get_clk_rate(struct dpu_kms *dpu_kms, char *clock_name)
 {
 	struct clk *clk;
 
 	clk = msm_clk_bulk_get_clock(dpu_kms->clocks, dpu_kms->num_clocks, clock_name);
 	if (!clk)
-		return -EINVAL;
+		return 0;
 
 	return clk_get_rate(clk);
 }

drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h

@@ -205,6 +205,6 @@ void dpu_disable_vblank(struct msm_kms *kms, struct drm_crtc *crtc);
  *
  * Return: current clock rate
  */
-u64 dpu_kms_get_clk_rate(struct dpu_kms *dpu_kms, char *clock_name);
+unsigned long dpu_kms_get_clk_rate(struct dpu_kms *dpu_kms, char *clock_name);
 
 #endif /* __dpu_kms_H__ */