Input: cs461x - convert documentation into ReST format

This file require minimum adjustments to be a valid ReST file.
Do it, in order to be able to parse it with Sphinx.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/input/cs461x.txt

-Preface.
+Crystal SoundFusion CS4610/CS4612/CS461 joystick
+================================================
+
+Preface
+-------
 
 This is a new low-level driver to support analog joystick attached to
 Crystal SoundFusion CS4610/CS4612/CS4615. This code is based upon