[LMB]: Fix initial lmb add region with a non-zero base

If we add to an empty lmb region with a non-zero base we will not
coalesce the number of regions down to one.  This causes problems on
ppc32 for the memory region as its assumed to only have one region.

We can fix this be easily specially casing the initial add to just
replace the dummy region.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>