leds: uleds: Fix potential buffer overread

leds: uleds: Fix potential buffer overread

The name string supplied by userspace is not guaranteed to be
null-terminated, so using strchr() on it might result in a buffer
overread. The same thing will happen when said string is used by
the LED class device.

Fix this by using strnchr() instead and explicitly check that
the name string is properly null-terminated.

Cc: stable@vger.kernel.org
Fixes: e381322b0190 ("leds: Introduce userspace LED class driver")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260524235553.189134-1-W_Armin@gmx.de
Signed-off-by: Lee Jones <lee@kernel.org>