drm/msm: Fix potential Oops in a6xx_gmu_rpmh_init()

There are two problems here:
1) The "seqptr" is used uninitalized when we free it at the end.
2) The a6xx_gmu_get_mmio() function returns error pointers.  It never
   returns true.

Fixes: 64245fc5 ("drm/msm/a6xx: use AOP-initialized PDC for a650")
Fixes: f8fc924e ("drm/msm/a6xx: Fix PDC register overlap")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20211004134530.GB11689@kiliSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a6xx_gmu.c

@@ -516,11 +516,11 @@ static void a6xx_gmu_rpmh_init(struct a6xx_gmu *gmu)
 	struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
 	struct platform_device *pdev = to_platform_device(gmu->dev);
 	void __iomem *pdcptr = a6xx_gmu_get_mmio(pdev, "gmu_pdc");
-	void __iomem *seqptr;
+	void __iomem *seqptr = NULL;
 	uint32_t pdc_address_offset;
 	bool pdc_in_aop = false;
 
-	if (!pdcptr)
+	if (IS_ERR(pdcptr))
 		goto err;
 
 	if (adreno_is_a650(adreno_gpu) || adreno_is_a660_family(adreno_gpu))
@@ -532,7 +532,7 @@ static void a6xx_gmu_rpmh_init(struct a6xx_gmu *gmu)
 
 	if (!pdc_in_aop) {
 		seqptr = a6xx_gmu_get_mmio(pdev, "gmu_pdc_seq");
-		if (!seqptr)
+		if (IS_ERR(seqptr))
 			goto err;
 	}