ASoC: doc: dapm: update section "DAPM Widget Events"

The example in this section is not in the kernel sources anymore. Replace
it with an up to date code fragment. Reword the initial paragraph. Remove
"Please" which is not standard practice in documentation.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20240426-dapm-docs-v2-11-87b07547eb5b@bootlin.com


Signed-off-by: Mark Brown <broonie@kernel.org>