staging: vt6655: Rename function MACbSafeTxOff

Rename function MACbSafeTxOff to vt6655_mac_safe_tx_off to avoid
CamelCase which is not accepted by checkpatch.pl. Remove unnecessary
declaration of function and make function static.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/50211bbdd866be93fe9ea912a433e56460bf7f28.1662890990.git.philipp.g.hortmann@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>