greybus: loopback: fix typo in comment

Alex previously post a patch to fix this typo. Somehow it fell through the
cracks in the meantime. Do it again 'stastic' is a word 'statistic' is not.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>