drm/panthor: Fix the panthor_gpu_coherency_init() error path

drm/panthor: Fix the panthor_gpu_coherency_init() error path

The panthor_gpu_coherency_init() call has been moved around, but the
error path hasn't been adjusted accordingly. Make sure we undo what
has been done before this call in case of failure.

Fixes: 7d5a3b22f5b5 ("drm/panthor: Call panthor_gpu_coherency_init() after PM resume()")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/dri-devel/4da470aa-4f84-460e-aff8-dabc8cc4da15@stanley.mountain/T/#t
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://lore.kernel.org/r/20250414130120.581274-1-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>