powerpc/powernv/sriov: perform null check on iov before dereferencing iov

Currently pointer iov is being dereferenced before the null check of iov
which can lead to null pointer dereference errors. Fix this by moving the
iov null check before the dereferencing.

Detected using cppcheck static analysis:
linux/arch/powerpc/platforms/powernv/pci-sriov.c:597:12: warning: Either
the condition '!iov' is redundant or there is possible null pointer
dereference: iov. [nullPointerRedundantCheck]
 num_vfs = iov->num_vfs;
           ^

Fixes: 052da31d ("powerpc/powernv/sriov: De-indent setup and teardown")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230608095849.1147969-1-colin.i.king@gmail.com

arch/powerpc/platforms/powernv/pci-sriov.c

@@ -594,12 +594,12 @@ static void pnv_pci_sriov_disable(struct pci_dev *pdev)
 	struct pnv_iov_data   *iov;
 
 	iov = pnv_iov_get(pdev);
-	num_vfs = iov->num_vfs;
-	base_pe = iov->vf_pe_arr[0].pe_number;
-
 	if (WARN_ON(!iov))
 		return;
 
+	num_vfs = iov->num_vfs;
+	base_pe = iov->vf_pe_arr[0].pe_number;
+
 	/* Release VF PEs */
 	pnv_ioda_release_vf_PE(pdev);