drm/msm/a6xx: Check for ERR or NULL before iounmap

pdcptr and seqptr aren't necessarily valid, check them before trying to
unmap them.

Changes in v2:
- None

Cc: Jordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: NJordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: NSean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190523171653.138678-3-sean@poorly.run

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

@@ -504,8 +504,10 @@ static void a6xx_gmu_rpmh_init(struct a6xx_gmu *gmu)
 	wmb();
 
 err:
-	devm_iounmap(gmu->dev, pdcptr);
-	devm_iounmap(gmu->dev, seqptr);
+	if (!IS_ERR_OR_NULL(pdcptr))
+		devm_iounmap(gmu->dev, pdcptr);
+	if (!IS_ERR_OR_NULL(seqptr))
+		devm_iounmap(gmu->dev, seqptr);
 }
 
 /*