drivers: char: use module_platform_driver_probe()

This patch converts the drivers to use the
module_platform_driver_probe() macro which makes the code smaller and
a bit simpler.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>