Input: pwm-beeper - remove calls to legacy pwm_request API

There are no more users of pwm-beeper driver in mainline relying on
this legacy API, so let's remove it and simplify the driver code.

Acked-by: Thierry Reding <thierry.reding@gmail.com>
Tested-by: David Lechner <david@lechnology.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>