staging: visorchipset: fix sparse warnings about static declaration

Some functions were prototyped as static but the actual definition
wasn't. While this is valid (the function is static because the two
declarations don't conflict and the first one is static), this makes
sparse unhappy and cause confusion of normal people too.

Signed-off-by: Vincent Bernat <vincent@bernat.im>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>