staging: greybus: remove unused kfifo_ts

As of commit 8e1d6c33 ("greybus: loopback: drop bus aggregate
calculation"), nothing ever reads from kfifo_ts, so there is no
reason to write to it or even allocate it any more.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>