staging: greybus: fix spelling mistake: "Inavlid" -> "Invalid"

Trivial fix to spelling mistake in dev_err error message

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Acked-by: Mark Greer <mgreer@animalcreek.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>