staging: vt6655: Cleanup and rename function MACvSaveContext

Rename function MACvSaveContext to vt6655_mac_save_context to avoid
CamelCase which is not accepted by checkpatch.pl. Remove unnecessary
declaration of function and make function static. Change declaration of
cxt_buf to shorten code.

Signed-off-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/f514711695f1eafde9996edcc246da2adcd5f9c5.1662890990.git.philipp.g.hortmann@gmail.com


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