pm_runtime_get_sync() increments the runtime PM usage counter even
the call returns an error code. Thus a corresponding decrement is
needed on the error handling path to keep the counter balanced.

Fix this by adding the missed function call.
Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>