gpu: nvgpu: Validate perfmon id count

Add a check against a too big perfmon id count.

Bug 200192125
Coverity ID 24285

Change-Id: I9b17081a1ea7243e6b57c0a95c59913cd8daf98b
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/1132966

drivers/gpu/nvgpu/gk20a/css_gr_gk20a.c

@@ -662,6 +662,10 @@ int gr_gk20a_css_attach(struct gk20a *g,
 	if (!cs_client)
 		return -EINVAL;
 
+	if (!perfmon_count ||
+	    perfmon_count > CSS_MAX_PERFMON_IDS - CSS_FIRST_PERFMON_ID)
+		return -EINVAL;
+
 	gr = &g->gr;
 	*cs_client = NULL;