i2c: mlxbf: Use str_read_write() helper

Remove hard-coded strings by using the str_read_write() helper.

Signed-off-by: Feng Wei <feng.wei8@zte.com.cn>
Signed-off-by: Shao Mingyin <shao.mingyin@zte.com.cn>
Link: https://lore.kernel.org/r/20250401192603311H5OxuFmUSbPc4VnQQkhZr@zte.com.cn


Signed-off-by: Andi Shyti <andi.shyti@kernel.org>