PCI MSI: Style cleanups

Cleanups (nearly based on checkpatch).

Before: total: 11 errors, 2 warnings, 0 checks, 842 lines checked
After:  total:  0 errors, 0 warnings, 0 checks, 842 lines checked

v2: fix it's/its mistakes in comment

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>