PCI: make bitfield unsigned

Fix sparse warning:

drivers/pci/pci.h:247:25: error: dubious one-bit signed bitfield

Signed-off-by: Bill Pemberton <[e-mail]>
CC: [e-mail]
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/pci/pci.h

···
 	int stu;	/* Smallest Translation Unit */
 	int qdep;	/* Invalidate Queue Depth */
 	int ref_cnt;	/* Physical Function reference count */
-	int is_enabled:1;	/* Enable bit is set */
+	unsigned int is_enabled:1;	/* Enable bit is set */
 };
 
 #ifdef CONFIG_PCI_IOV