drm/msm/a6xx: No zap shader is not an error

Depending on platform firmware, a zap shader may not be required to take
the GPU out of secure mode on boot, in which case we can just write
RBBM_SECVID_TRUST_CNTL directly.  Which we *mostly* handled, but missed
clearing 'ret' resulting that hw_init() returned an error on these
devices.

Fixes: abccb9fe ("drm/msm/a6xx: Add zap shader load")
Acked-by: Jordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190508130726.27557-1-robdclark@gmail.com

drivers/gpu/drm/msm/adreno/a6xx_gpu.c

@@ -527,6 +527,7 @@ static int a6xx_hw_init(struct msm_gpu *gpu)
 		dev_warn_once(gpu->dev->dev,
 			"Zap shader not enabled - using SECVID_TRUST_CNTL instead\n");
 		gpu_write(gpu, REG_A6XX_RBBM_SECVID_TRUST_CNTL, 0x0);
+		ret = 0;
 	}
 
 out: