staging/mei: mei-amt-version - make all function static and used

This patch eliminates following type of warnings
warning: no previous prototype for '...func...' [-Wmissing-prototypes]

For this is a single file example lets make all API-like functions
be static.
Since all static functions should be used so let's call
to amt_host_if_deinit() even if in this example it's not really necessary

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>