staging: vt6655: fix camelcase in PortOffset

Replace camel case variable PortOffset with snake case
variable port_offset.

Signed-off-by: Tommaso Merciai <tomm.merciai@gmail.com>
Link: https://lore.kernel.org/r/20211005205702.14029-4-tomm.merciai@gmail.com


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