ref-manual: Edits to boot-directdisk class.

(From yocto-docs rev: b2b305a3088423f8f833bd17b41cdbe7a4cc34cd)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-classes.xml

@@ -232,7 +232,7 @@
     <title><filename>boot-directdisk.bbclass</filename></title>
 
     <para>
-        The boot direct disk (<filename>boot-directdisk</filename>) class
+        The <filename>boot-directdisk</filename> class
         creates an image that can be placed directly onto a hard disk using
         <filename>dd</filename> and then booted.
         The image uses SYSLINUX.