trace: Reduce the default for TRACE_EARLY_CALL_DEPTH_LIMIT

This is a silly value at present, since U-Boot's call depth never reaches
200. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index 06c873c..83e5edd 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -368,7 +368,7 @@
 config TRACE_EARLY_CALL_DEPTH_LIMIT
 	int "Early trace call depth limit"
 	depends on TRACE_EARLY
-	default 200
+	default 15
 	help
 	  Sets the maximum call depth up to which function calls are recorded
 	  during early tracing.