VT-d: fix mask applied to DMIBAR in desktop chipset XSA-59 workaround

In commit  ("VT-d: suppress UR signaling for desktop chipsets")
the mask applied to the value read from DMIBAR is to narrow, only the
comment accompanying it was correct. Fix that and tag the literal
number as "long" at once to avoid eventual compiler warnings.

The widest possible value so far is 39 bits; all chipsets covered here
but having less than this number of bits have the remaining bits marked
reserved (zero), and hence there's no need for making the mask chipset
specific.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -467,7 +467,7 @@ void pci_vtd_quirk(const struct pci_dev 
     case 0xc00: case 0xc04: case 0xc08: /* Haswell */
         bar = pci_conf_read32(seg, bus, dev, func, 0x6c);
         bar = (bar << 32) | pci_conf_read32(seg, bus, dev, func, 0x68);
-        pa = bar & 0x7fffff000; /* bits 12...38 */
+        pa = bar & 0x7ffffff000UL; /* bits 12...38 */
         if ( (bar & 1) && pa &&
              page_is_ram_type(paddr_to_pfn(pa), RAM_TYPE_RESERVED) )
         {