Staging: lustre: include: Move function prototypes

Functions:
struct obd_export *class_export_get(struct obd_export *exp);
void class_export_put(struct obd_export *exp)
are being used in macros that are converted into static inline
functions, therefore move function prototypes to avoid build
error in later patches.

Signed-off-by: Ksenija Stanojevic <ksenija.stanojevic@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>