serial: hp300: Remove obsolete comments

setup_serial_console() is obsolete and has been superseded by
early_serial_setup() which is called at the end of the function.

The IA64 arch does not call this function; only the m68k arch setup
calls this function.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>