cml1.bbclass: Fix return code handling in do_menuconfig()

cml1.bbclass: Fix return code handling in do_menuconfig()

On my system, doing "bitbake -c menuconfig busybox" pops up
a gnome-terminal, I can see that the compilation starts but then the
terminal automatically exits.

It turns out I don't have ncurses development package installed on my host,
and OE's host sysroot isn't being passed to gcc, so compilation fails.
The window automatically closes before I can read the error message
since the '$' in the return code check needs to be escaped.

Make sure the user can read the error message by properly checking the
return code.

(From OE-Core rev: a2241a92fc48e4286de17b23124a9e2f0fd8185b)

Signed-off-by: Jacob Kroon <jacob.kroon@mikrodidakt.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>