Mk/bsd.gecko.mk: Fix indentation

[pre-commit] ERROR: bsd.gecko.mk is not properly indented -- please
use /tmp/check_indentations-bsd.gecko.mk.n87gemd4sB/bsd.gecko.mk which
was created using Tools/scripts/indent_make_if.pl

Reported by: 'check_mk_indentations' pre-commit hook