Staging: lustre: Fix externs should be avoided in .c

This patch moves extern declaration to ldlm_internal.h.
Remove prototype from ldlm_lockd.c and ldlm_lock.c.
Issue addressed by checkpatch.pl.

Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>