pwm: pwm-tiecap: Update dt binding document to use proper unit address

Replace unit address from 0 to the proper physical address. Also insure
that the unit address matches the reg property address.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>