staging: olpc_dcon: replace remaining calls to i2c_smbus_read/write

Use dcon_read and dcon_write; shorter, and understands the dcon_priv
struct.  This transition was started long ago.  This converts the
last few i2c_smbus_* callers.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>