PCI: Add mask bit definition for MSI-X table

Then we can use it instead of magic number 1.

Reviewed-by: Hidetoshi Seto <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Signed-off-by: Sheng Yang <[e-mail]>
Signed-off-by: Jesse Barnes <[e-mail]>

drivers/pci/msi.c

···
 	u32 mask_bits = desc->masked;
 	unsigned offset = desc->msi_attrib.entry_nr * PCI_MSIX_ENTRY_SIZE +
 						PCI_MSIX_ENTRY_VECTOR_CTRL;
-	mask_bits &= ~1;
-	mask_bits |= flag;
+	mask_bits &= ~PCI_MSIX_ENTRY_CTRL_MASKBIT;
+	if (flag)
+		mask_bits |= PCI_MSIX_ENTRY_CTRL_MASKBIT;
 	writel(mask_bits, desc->mask_base + offset);
 
 	return mask_bits;

include/linux/pci_regs.h

···
 #define  PCI_MSIX_ENTRY_UPPER_ADDR	4
 #define  PCI_MSIX_ENTRY_DATA		8
 #define  PCI_MSIX_ENTRY_VECTOR_CTRL	12
+#define   PCI_MSIX_ENTRY_CTRL_MASKBIT	1
 
 /* CompactPCI Hotswap Register */