drm/i915/gt: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200311073256.6535-1-tiwai@suse.de

drivers/gpu/drm/i915/gt/intel_engine_cs.c

@@ -1381,13 +1381,13 @@ static void intel_engine_print_registers(struct intel_engine_cs *engine,
 			char hdr[160];
 			int len;
 
-			len = snprintf(hdr, sizeof(hdr),
+			len = scnprintf(hdr, sizeof(hdr),
 					"\t\tActive[%d]: ",
 					(int)(port - execlists->active));
 			if (!i915_request_signaled(rq)) {
 				struct intel_timeline *tl = get_timeline(rq);
 
-				len += snprintf(hdr + len, sizeof(hdr) - len,
+				len += scnprintf(hdr + len, sizeof(hdr) - len,
 						 "ring:{start:%08x, hwsp:%08x, seqno:%08x, runtime:%llums}, ",
 						 i915_ggtt_offset(rq->ring->vma),
 						 tl ? tl->hwsp_offset : 0,
@@ -1398,7 +1398,7 @@ static void intel_engine_print_registers(struct intel_engine_cs *engine,
 				if (tl)
 					intel_timeline_put(tl);
 			}
-			snprintf(hdr + len, sizeof(hdr) - len, "rq: ");
+			scnprintf(hdr + len, sizeof(hdr) - len, "rq: ");
 			print_request(m, rq, hdr);
 		}
 		for (port = execlists->pending; (rq = *port); port++) {