p54: drop device reference count if fails to enable device

The function p54p_probe takes an extra reference count of the PCI
device. However, the extra reference count is not dropped when it fails
to enable the PCI device. This patch fixes the bug.

Cc: stable@vger.kernel.org
Signed-off-by: Pan Bian <bianpan2016@163.com>
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>