The pwm-scaler0 and pwm-scaler1 clocks have their
.id field set to -1 as they are not referenced to
any specific device. However, parts of the pwm-clock
code used the .id field to identify which scaler
clock was being used.

Fix the problem by comparing against the pointer to
the clock to identify the scalers.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>