msm: kgsl: add a kgsl_readtimestamp() wrapper

Calling this device function directly from the function
table is unnecessarily verbose, and done fairly often.

Change-Id: Ib9d75b31dfab8fb4ccced46fe62a08a98da8c94f
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>
diff --git a/drivers/gpu/msm/adreno_ringbuffer.c b/drivers/gpu/msm/adreno_ringbuffer.c
index 8d900b0..3d46221 100644
--- a/drivers/gpu/msm/adreno_ringbuffer.c
+++ b/drivers/gpu/msm/adreno_ringbuffer.c
@@ -928,8 +928,8 @@
 			" context id is invalid.\n");
 		return -EINVAL;
 	}
-	retired_timestamp = device->ftbl->readtimestamp(device, context,
-				KGSL_TIMESTAMP_RETIRED);
+	retired_timestamp = kgsl_readtimestamp(device, context,
+					       KGSL_TIMESTAMP_RETIRED);
 	KGSL_DRV_ERR(device, "GPU successfully executed till ts: %x\n",
 			retired_timestamp);
 	/*