Revert "rt2x00pci: Use PCI MSIs whenever possible"

This reverts commit 9483f40d.

Some devices stop to connect with above commit, see:
https://bugzilla.kernel.org/show_bug.cgi?id=61621



Since there is no clear benefit of having MSI enabled, just revert
change to fix the problem.

Cc: stable@vger.kernel.org # 3.11+
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>