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

In the Linux kernel, the following vulnerability has been resolved: 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; ^