docs: sound: kernel-api: writing-an-alsa-driver.rst: replace some characters

The conversion tools used during DocBook/LaTeX/html/Markdown->ReST
conversion and some cut-and-pasted text contain some characters that
aren't easily reachable on standard keyboards and/or could cause
troubles when parsed by the documentation build system.

Replace the occurences of the following characters:

	- U+00a0 (' '): NO-BREAK SPACE
	  as it can cause lines being truncated on PDF output
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/21abe5fa495a05ac1f998ed66184a77e19ac89cc.1626947264.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sound/kernel-api/writing-an-alsa-driver.rst

@@ -3368,7 +3368,7 @@ This ensures that the device can be closed and the driver unloaded
 without losing data.
 
 This callback is optional. If you do not set ``drain`` in the struct
-snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds
+snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds
 instead.
 
 Miscellaneous Devices