Previously the timers where based on the classic timers, giving a too
coarse resolution on systems with configs of less than 1000 HZ.

This patch changes the rs485 timers to hrtimers.
Signed-off-by: NRafael Gago Castano <rgc@hms.se>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>