ref-manual: Fixed title name in link.
The actual title of the sdk-manual does not include the word
"Manual". So, the reference to the book should terminate with the
word "manual" in lower case.
(From yocto-docs rev: 41bc85776f0b172fc243b6e5a5ca13b72e8399e5)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>