[LMB]: Fix lmb allocation regression.

Changeset d9024df0 ("[LMB] Restructure
allocation loops to avoid unsigned underflow") removed the alignment
of the 'size' argument to call lmb_add_region() done by __lmb_alloc_base().

In doing so it reintroduced the bug fixed by changeset
eea89e13 ("[LMB]: Fix bug in
__lmb_alloc_base().").

This puts it back.

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