The size might be 64 bit, so use ilog2() instead of __ilog2() or
__ilog2_u64().

ilog2() can select 32bit or 64bit function automatically.
Signed-off-by: NRoy Zang <tie-fei.zang@freescale.com>
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>