x86/MSI: don't risk division by zero

The check in question is redundant with the one in the immediately
following if(), where dividing by zero gets carefully avoided.

Spotted-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -635,7 +635,7 @@ static u64 read_pci_mem_bar(u16 seg, u8 
             return 0;
         base = pos + PCI_SRIOV_BAR;
         vf -= PCI_BDF(bus, slot, func) + offset;
-        if ( vf < 0 || (vf && vf % stride) )
+        if ( vf < 0 )
             return 0;
         if ( stride )
         {