amdkfd: actually allocate longs for the pasid bitmask

Commit "amdkfd: use sizeof(long) granularity for the pasid bitmask" calculated
the number of longs it will need, but ended up allocating that number of
bytes rather than longs.

Fix that silly error and allocate the amount of data really required.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>