USB: serial: keyspan: Removed unrequired parentheses.

Changes to conform with checkpatch.sh script. - return is not a
function, parentheses not required. Removed 1 checkpatch.sh error.

Signed-off-by: Ben Minerds <puzzleduck@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>