docs: firmware-guide: acpi: dsd: graph.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
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/a65b04a5cf341cff02d4b514dd4889b4fa4f94b8.1626947264.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/firmware-guide/acpi/dsd/graph.rst

@@ -159,7 +159,7 @@ References
 
 [2] Devicetree. https://www.devicetree.org, referenced 2016-10-03.
 
-[3] Documentation/devicetree/bindings/graph.txt
+[3] Documentation/devicetree/bindings/graph.txt
 
 [4] Device Properties UUID For _DSD.
     https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf,