get_vm_area() only accepts VM_* flags, not GFP_*.

And according to the doc of get_vm_area(), here should be
VM_ALLOC.
Signed-off-by: NWANG Cong <amwang@redhat.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>