docs: unaligned-memory-access.txt: use a lowercase title

As all other titles at the documentation, use lower case
for its title.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/unaligned-memory-access.txt

 =========================
-UNALIGNED MEMORY ACCESSES
+Unaligned Memory Accesses
 =========================
 
 :Author: Daniel Drake <dsd@gentoo.org>,