Staging: me4000: make file_operations const

This eliminates checkpatch.pl warnings, that struct file_operations is
usually const.  The structs me4000_ai_fops_array and
me4000_ao_fops_array are not modified and thus also made const.

Signed-off-by: Andre Haupt <andre@bitwigglers.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>