staging: wilc1000: declare 'fops' as const

Change the declaration of the file_operations structure 'fops' into
const as suggested by checkpatch.

WARNING: struct file_operations should normally be const

Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>