With the recent change to avoid masking MSIs using the MSI enable bit, devices
without an MSI mask bit will have their MSI capability always enabled when MSI
is in use, so we need to restore it regardless of the mask bit state.

Fixes kernel bz 11178.
Acked-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>