Documentation: arm: marvell: Add link to Orion Functional Errata document

Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20210704181110.9254-1-pali@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/arm/marvell.rst

@@ -21,6 +21,7 @@ Orion family
                - Datasheet: https://web.archive.org/web/20210124231420/http://csclub.uwaterloo.ca/~board/ts7800/MV88F5182-datasheet.pdf
                - Programmer's User Guide: https://web.archive.org/web/20210124231536/http://csclub.uwaterloo.ca/~board/ts7800/MV88F5182-opensource-manual.pdf
                - User Manual: https://web.archive.org/web/20210124231631/http://csclub.uwaterloo.ca/~board/ts7800/MV88F5182-usermanual.pdf
+               - Functional Errata: https://web.archive.org/web/20210704165540/https://www.digriz.org.uk/ts78xx/88F5182_Functional_Errata.pdf
         - 88F5281
 
                - Datasheet: https://web.archive.org/web/20131028144728/http://www.ocmodshop.com/images/reviews/networking/qnap_ts409u/marvel_88f5281_data_sheet.pdf