drm/msm/gpu: Fix a couple memory leaks in debugfs

The msm_gpu_open() function should free "show_priv" on error or it
causes static checker warnings.

Fixes: 4f776f45 ("drm/msm/gpu: Convert the GPU show function to use the GPU state")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>