MIPS: fix vdso different address spaces

sparse report build warning as follows:
arch/mips/vdso/vdso-n32-image.c:13:35:
incorrect type in assignment (different address spaces) @@
expected void *[usertype] vdso @@     got void [noderef] <asn:1> * @@
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sunguoyun <sunguoyun@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/vdso/genvdso.c

@@ -260,7 +260,7 @@ int main(int argc, char **argv)
 	fprintf(out_file, "	if (vdso_image.size != new_size)\n");
 	fprintf(out_file, "		return -EINVAL;\n");
 	fprintf(out_file, "	current->mm->context.vdso =\n");
-	fprintf(out_file, "	(void __user *)(new_vma->vm_start);\n");
+	fprintf(out_file, "	(void *)(new_vma->vm_start);\n");
 	fprintf(out_file, "	return 0;\n");
 	fprintf(out_file, "}\n");