lbmk: don't use status for unconditional returns

in cases where lbmk must always return from a function,
there are some cases where it relies on non-zero exit
status, which in practise is always the case, but may
change in the future if the relevant part is modified

e.g. do_something && return 0

the proper form is:
do_something
return 0

also do this for unconditional exits

Signed-off-by: Leah Rowe <leah@libreboot.org>