drm/nouveau: replace snprintf() with scnprintf() in nvkm_snprintbf()

drm/nouveau: replace snprintf() with scnprintf() in nvkm_snprintbf()

snprintf() returns the number of characters that *would* have been
written, which can overestimate how much you actually wrote to the
buffer in case of truncation. That leads to 'data += this' advancing
the pointer past the end of the buffer and size going negative.

Switching to scnprintf() prevents potential buffer overflows and ensures
consistent behavior when building the output string.

Signed-off-by: Seyediman Seyedarab <ImanDevel@gmail.com>
Link: https://lore.kernel.org/r/20250724195913.60742-1-ImanDevel@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>