lmb: Fix inconsistent alignment of size argument.

When allocating, if we will align up the size when making
the reservation, we should also align the size for the
check that the space is actually available.

The simplest thing is to just aling the size up from
the beginning, then we can use plain 'size' throughout.

Signed-off-by: David S. Miller <davem@davemloft.net>