xen/pci: fix violations of MISRA C:2012 Rule 7.2

The xen sources contains violations of MISRA C:2012 Rule 7.2 whose
headline states:
"A 'u' or 'U' suffix shall be applied to all integer constants
that are represented in an unsigned type".

Add the 'U' suffix to integers literals with unsigned type and also to other
literals used in the same contexts or near violations, when their positive
nature is immediately clear. The latter changes are done for the sake of
uniformity.

Signed-off-by: Gianluca Luparini <gianluca.luparini@bugseng.com>
Signed-off-by: Simone Ballarin <simone.ballarin@bugseng.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/passthrough/pci.c

@@ -990,8 +990,8 @@ bool_t __init pci_device_detect(u16 seg, u8 bus, u8 dev, u8 func)
 
     vendor = pci_conf_read32(PCI_SBDF(seg, bus, dev, func), PCI_VENDOR_ID);
     /* some broken boards return 0 or ~0 if a slot is empty: */
-    if ( (vendor == 0xffffffff) || (vendor == 0x00000000) ||
-         (vendor == 0x0000ffff) || (vendor == 0xffff0000) )
+    if ( (vendor == 0xffffffffU) || (vendor == 0x00000000U) ||
+         (vendor == 0x0000ffffU) || (vendor == 0xffff0000U) )
         return 0;
     return 1;
 }