i3c: replace deprecated strncpy

i3c: replace deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

We expect adap->name to be NUL-terminated based on i2c_adapter name use:
| dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);

NUL-padding does not seem to be required as `master` is zero-allocated
and `i3c_master_to_i2c_adapter` simply returns a field from within
`master`:
|       master = devm_kzalloc(dev, sizeof(*master), GFP_KERNEL);
...
|      	struct i2c_adapter *adap = i3c_master_to_i2c_adapter(master);
...
|       static struct i2c_adapter *
|       i3c_master_to_i2c_adapter(struct i3c_master_controller *master)
|       {
|       	return &master->i2c;
|       }

This means that `adap->name` should already be filled with NUL-bytes.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230921-strncpy-drivers-i3c-master-c-v1-1-9fdb8d8169e1@google.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>