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>