ath79: rename tplink-loader-okli to tplink-safeloader-okli

This renames Device/tplink-loader-okli to Device/tplink-safeloader-okli
since the latter more accurately describes the combination of
tplink-safeloader and loader-okli use there. The old version might
be confused with other uses of the okli loader.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>