docs: userspace-api: media: v4l: 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
	- U+2014 ('—'): EM DASH
	- U+2019 ('’'): RIGHT SINGLE QUOTATION MARK

Note that Sphinx auto-translates '---' into EM DASH.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>