drm/msm: free the IRQ during GPU cleanup

Free the IRQ in msm_gpu_cleanup. This is required
to avoid failures from devm_request_irq on subsequent
retries to load the GPU in case the previous attempt
failed somewhere after successful call to
devm_request_irq.

Change-Id: I90d98199a1d7867e3f7b51f8e2293fa28e4612fa
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>