util: Fix error path for virPCIGetVirtualFunctions

If we get to the error: label and clear out the *virtual_functions[]
pointers and then return w/ error to the caller - the caller has it's
own cleanup of the same array in the out: label which is keyed off the
value of num_virt_fns, which wasn't reset to 0 in the called function
leading to a possible problem.

Just clear the value (found by Coverity)
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

src/util/virpci.c

@@ -2573,6 +2573,7 @@ virPCIGetVirtualFunctions(const char *sysfs_path,
     for (i = 0; i < *num_virtual_functions; i++)
         VIR_FREE((*virtual_functions)[i]);
     VIR_FREE(*virtual_functions);
+    *num_virtual_functions = 0;
     goto cleanup;
 }