greybus: timesync: Make printout consitent with other greybus messages

The current printout on a TimeSync ping doesn't actually contain the word
greybus and uses the word ping-time in the print string, something that
appears nowhere in our official documentation on this feature. This patch
changes the format string to contain 'greybus' and 'frametime' to bring the
TimeSync printout more in-line with other greybus kernel log strings.

before:
timesync ping-time: ap=8632564 1-svc=8630712 greybus1=8633031 1-8.8=8633026

after:
greybus frametime: ap=8632564 1-svc=8630712 greybus1=8633031 1-8.8=8633026

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