staging/lustre: clean function declaration in super25.c up

We get 1 warning when building kernel with W=1:
drivers/staging/lustre/lustre/obdclass/obd_config.c:719:6: warning: no previous prototype for 'lustre_register_client_process_config' [-Wmissing-prototypes]

In fact, this function is declared in
drivers/staging/lustre/lustre/llite/super25.c, but should be
moved into a header file, thus can be recognized in other file.

So this patch moves the declaration into
drivers/staging/lustre/lustre/include/lprocfs_status.h.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>