mei: make mei_io_list_flush static

mei_io_list_flush is used only in client.c
so make it local to the file and mark static.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>