PCI/MSI: bugfix/utilize for msi_capability_init()

This patch fix a following bug and does a cleanup.

bug:
	commit 5993760f
	had a wrong change (since is_64 is boolean[0|1]):

-               pci_write_config_dword(dev,
-                       msi_mask_bits_reg(pos, is_64bit_address(control)),
-                       maskbits);
+               pci_write_config_dword(dev, entry->msi_attrib.is_64, maskbits);

utilize:
	Unify separated if (entry->msi_attrib.maskbit) statements.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: "Jike Song" <albcamus@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>