greybus: timesync: Bugfix ping should not result in -EAGAIN

gb_timesync_schedule_synchronous() is currently making a synchronous
FrameTime synchronization happen. It does a wait_event_interruptible() and
then goes to check the status of the state-machine. Occasionally the state
indicates PING - which is a completely valid state and should result in a
result code of 0 not -EAGAIN. This patch fixes by making
__gb_timesync_get_status() return 0 instead of -EAGAIN for the PING state.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: David Lin <dtwlin@google.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>