pwm: Correct parameter name in header for *pwm_get() functions

To synchronize the header file definition and the actual code. In the code
the consumer parameter is named as con_id, change the header file and replace
consumer -> con_id in the parameter list.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Ackedy-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Bryan Wu <cooloney@gmail.com>