i2c: amd-asf: Fix uninitialized variables issue in amd_asf_process_target

i2c: amd-asf: Fix uninitialized variables issue in amd_asf_process_target

The len variable is not initialized, which may cause the for loop to
behave unexpectedly.

Fixes: 9b25419ad397 ("i2c: amd-asf: Add routine to handle the ASF slave process")
Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>