[OPTIM] ebtree: ebmb_lookup: reduce stack usage by moving the return code out of...

[OPTIM] ebtree: ebmb_lookup: reduce stack usage by moving the return code out of the loop

(from ebtree 6.0.5)

Last bugfix has introduced a de-optimization in the lookup function because
it artificially extended the scope of some local variables, which resulted in
higher stack usage and more numerous moves between stack and registers.

We can reduce that by moving the return code out of the loop, because gcc
notices that it never needs both "troot" and "node" at the same time and
can use the same register for both. Doing so has reduced the code size by
39 bytes for the lookup function alone, and has sensibly reduced the
instruction dependencies caused by data moves.
(cherry picked from commit 59be3cdb96296b65a57aff30cc203269f9a94ebe)

It should be backported to 1.4 if previous ebtree fix is backported.