apps: zynqmp_r5: check NULL pointer in mmap()

Check if pointer is NULL in mmap() before writing to it.

Signed-off-by: Wendy Liang <wendy.liang@xilinx.com>

apps/machine/zynqmp_r5/zynqmp_r5_a53_rproc.c

@@ -147,7 +147,8 @@ zynqmp_r5_a53_proc_mmap(struct remoteproc *rproc, metal_phys_addr_t *pa,
 	remoteproc_add_mem(rproc, mem);
 	*pa = lpa;
 	*da = lda;
-	*io = tmpio;
+	if (io)
+		*io = tmpio;
 	return metal_io_phys_to_virt(tmpio, mem->pa);
 }