x86/MSI: drop bogus NULL check from pci_restore_msi_state()

Commit 372900faf8 ("x86/MSI-X: reduce fiddling with control register
during restore") introduced de-references of pdev before it gets
checked against NULL. Instead of deferring the de-references, drop
the pointless check - both call sites do that check already.

Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -1354,9 +1354,6 @@ int pci_restore_msi_state(struct pci_dev
     if ( !use_msi )
         return -EOPNOTSUPP;
 
-    if ( !pdev )
-        return -EINVAL;
-
     ret = xsm_resource_setup_pci(XSM_PRIV,
                                 (pdev->seg << 16) | (pdev->bus << 8) |
                                 pdev->devfn);