staging: fbtft: Fix multi-line comment style

Thus use the preferred style for multi-line coments as
mentioned in Documentation/CodingStyle.

It also silences 'Block comments use * on subsequent lines'
checkpatch.pl warnings.

Signed-off-by: Cristina Moraru <cristina.moraru09@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>