alpha: fix typo in recent early vmalloc change

Impact: fix build

Add missing 'o' in variable name.  Compile tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>