serial: 8250-mtk: Fix reference leak in mtk8250_probe

serial: 8250-mtk: Fix reference leak in mtk8250_probe

[ Upstream commit 6e4e636e0e3e0b5deffc5e233adcb2cd4e68f2d0 ]

The pm_runtime_enable will increase power disable depth.
Thus a pairing decrement is needed on the error handling
path to keep it balanced according to context.

Fixes: e32a83c70cf98 ("serial: 8250-mtk: modify mtk uart power and clock management")
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Link: https://lore.kernel.org/r/20201119141126.168850-1-zhangqilong3@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>