drivers/misc/sgi-gru: make functions static

The functions gru_get_cb_exception_detail_str() and gru_abort() were
only called locally from that file. We can make them static.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>