ion: Fix pool refill error

When performing secure pool allocations, it's possible to
spuriously trigger pool refill attempts for the cached and
uncached pools. Fix this by adding a check to see if we're
performing a secure allocation or not, before refilling a pool.

Change-Id: I9a415a302ca92790e6a793784020b09dea6a86e1
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>