Make local of child pointer.
Make local of child pointer.

In capnp it is relatively expensive to follow a pointer, so don't do
extra work if it can be avoided.

Signed-off-by: Keith Rothman <1bc19627a439baf17510dc2d0b2d250c96d445a5@users.noreply.github.com>

SymbiFlow/uxsdcxx,SymbiFlow/uxsdcxx