drm/nouveau: nouveau: use correct string length

gcc-8 reports

drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c: In function 'nvkm_perfmon_mthd':
include/linux/string.h:265:9: error: '__builtin_strncpy' specified bound 64 equals destination size [-Werror=stringop-truncation]

We need one less byte or call strlcpy() to make it a
nul-terminated string.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ben Skeggs <bskeggs@redhat.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));
+		strncpy(args->v0.name, dom->name, sizeof(args->v0.name) - 1);
 
 		/* Currently only global counters (PCOUNTER) are implemented
 		 * but this will be different for local counters (MP). */
@@ -514,7 +514,7 @@ nvkm_perfmon_mthd_query_signal(struct nvkm_perfmon *perfmon,
 				 "/%s/%02x", dom->name, si);
 		} else {
 			strncpy(args->v0.name, sig->name,
-				sizeof(args->v0.name));
+				sizeof(args->v0.name) - 1);
 		}
 
 		args->v0.signal = si;
@@ -572,7 +572,7 @@ 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));
+		strncpy(args->v0.name, src->name, sizeof(args->v0.name) - 1);
 	}
 
 	if (++si < source_nr) {