classes/binconfig: fix indentation in python function

classes/binconfig: fix indentation in python function

If we don't fix this, the recently added dependency from
do_populate_sysroot on functions in SYSROOT_PREPROCESS_FUNCS in
staging.bbclass triggers warnings that the get_binconfig_mangle
function contains tabs for all recipes that inherit binconfig.

Related to fix for [YOCTO #5852].

(From OE-Core rev: a30a204270ee5b91d9c0904d3c3dda34bdb9ce1c)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>