staging: lustre: fld: fixed symbol was not declared

Fixes the sparse warning:
"warning: symbol 'fld_type_proc_dir' was not declared. Should it be static?"

Also removes initialization to NULL.

Signed-off-by: Brian Vandre <bvandre@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>