driver: pwm: infineon: Use PWM buffer updates

Change PWM to use buffers registers instead of writing period
and compare directly.  This addressses an issue when updating
period to a value less than current counter, as demonstrated
in the blinky_pwm sample running on the CYW920829M2EVK_02
board.

Signed-off-by: John Batch <john.batch@infineon.com>