BUG/MEDIUM: trace: fix a typo causing an incorrect startup error

Since commit 88ebd40 ("MINOR: trace: add allocation of buffer-sized
trace buffers") we have a trace buffer allocated at boot time. But
there was a copy-paste error there making the test verify that the
trash was allocated instead of the trace buffer. The result is that
depending on the link order either the test will succeed or fail,
preventing haproxy from starting at all.

No backport is needed.
diff --git a/src/trace.c b/src/trace.c
index 220bf66..06fec4a 100644
--- a/src/trace.c
+++ b/src/trace.c
@@ -37,7 +37,7 @@
 static int alloc_trace_buffers_per_thread()
 	chunk_init(&trace_buf, my_realloc2(trace_buf.area, global.tune.bufsize), global.tune.bufsize);
-	return !!trash.area;
+	return !!trace_buf.area;
 static void free_trace_buffers_per_thread()