staging/lustre/o2iblnd: fix is_vmalloc_addr build warning

I got this building Lustre:
drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd_cb.c: In function ‘kiblnd_kvaddr_to_page’:
drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd_cb.c:532:2: warning: passing argument 1 of ‘is_vmalloc_addr’ makes pointer from integer without a cast [enabled by default]

Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd_cb.c

@@ -529,7 +529,7 @@ kiblnd_kvaddr_to_page (unsigned long vaddr)
 {
 	struct page *page;
 
-	if (is_vmalloc_addr(vaddr)) {
+	if (is_vmalloc_addr((void *)vaddr)) {
 		page = vmalloc_to_page ((void *)vaddr);
 		LASSERT (page != NULL);
 		return page;