ALSA: docs: writing-an-alsa-driver.rst: polishing

- Update some outdated info
- Language fixes
- Whitespace/formatting fixes
- Prefer attached over stand-alone '::'

[ dropped a trailing white space in the patch -- tiwai ]

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

Link: https://lore.kernel.org/r/20230421112751.990244-1-oswald.buddenhagen@gmx.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>