i2c: xiic: Fix kerneldoc warnings

Fix the below warning by adding the description of clock and dev.

drivers/i2c/busses/i2c-xiic.c:57: info: Scanning doc for struct xiic_i2c
drivers/i2c/busses/i2c-xiic.c:84: warning: Function parameter or member
'dev' not described in 'xiic_i2c'
drivers/i2c/busses/i2c-xiic.c:84: warning: Function parameter or member
'clk' not described in 'xiic_i2c'

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>