Staging: lustre: obdclass: Declare function as static

Declare the function cache_stats_print as static since it is used
only  in this file. Used grep to find occurences. Problem found using
sparse.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>