media: venus: hfi: avoid null dereference in deinit

If venus_probe fails at pm_runtime_put_sync the error handling first
calls hfi_destroy and afterwards hfi_core_deinit. As hfi_destroy sets
core->ops to NULL, hfi_core_deinit cannot call the core_deinit function
anymore.

Avoid this null pointer derefence by skipping the call when necessary.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>