Add description for 'data' parameter and drop unused 'irq' memeber.

Here is the warnings:
drivers/i2c/busses/i2c-meson.c:103: warning: No description found for
parameter 'data'
drivers/i2c/busses/i2c-meson.c:103: warning: Excess struct member 'irq'
description in 'meson_i2c'
Reported-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>