drm/nouveau/pm: refactor deprecated strncpy

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

We should prefer more robust and less ambiguous string interfaces.

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 [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
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>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230914-strncpy-drivers-gpu-drm-nouveau-nvkm-engine-pm-base-c-v1-1-4b09ed453f84@google.com

drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c

@@ -462,7 +462,7 @@ nvkm_perfmon_mthd_query_domain(struct nvkm_perfmon *perfmon,
 
 		args->v0.id         = di;
 		args->v0.signal_nr  = nvkm_perfdom_count_perfsig(dom);
-		strncpy(args->v0.name, dom->name, sizeof(args->v0.name) - 1);
+		strscpy(args->v0.name, dom->name, sizeof(args->v0.name));
 
 		/* Currently only global counters (PCOUNTER) are implemented
 		 * but this will be different for local counters (MP). */
@@ -513,8 +513,7 @@ nvkm_perfmon_mthd_query_signal(struct nvkm_perfmon *perfmon,
 			snprintf(args->v0.name, sizeof(args->v0.name),
 				 "/%s/%02x", dom->name, si);
 		} else {
-			strncpy(args->v0.name, sig->name,
-				sizeof(args->v0.name) - 1);
+			strscpy(args->v0.name, sig->name, sizeof(args->v0.name));
 		}
 
 		args->v0.signal = si;
@@ -572,7 +571,7 @@ nvkm_perfmon_mthd_query_source(struct nvkm_perfmon *perfmon,
 
 		args->v0.source = sig->source[si];
 		args->v0.mask   = src->mask;
-		strncpy(args->v0.name, src->name, sizeof(args->v0.name) - 1);
+		strscpy(args->v0.name, src->name, sizeof(args->v0.name));
 	}
 
 	if (++si < source_nr) {