pch_uart: Fix MSI setting issue

The following patch (MSI setting) is not enough.

commit e463595fd9c752fa4bf06b47df93ef9ade3c7cf0
Author: Alexander Stein <alexander.stein@systec-electronic.com>
Date:   Mon Jul 4 08:58:31 2011 +0200

    pch_uart: Add MSI support

    Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
To enable MSI mode, PCI bus-mastering must be enabled.
This patch enables the setting.

cc: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>