msm: kgsl: Move ringbuffer_init after device_platform_probe

It makes more sense to allocate and initialize the ringbuffer
after the device_platform_probe.

Change-Id: I1d98949a3da10b4dd4fbc126bb091029e0f9e49a
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>