staging: line6: fix quoted string across lines in midibuf.c

Checkpatch warns when quoted strings are split across lines.  The
rationale is that quoted strings should be left on a single line so that
grep works.  (The 80 character line limit does not apply to quoted
strings.)

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>