target/espressif: fix clang report on list use

It looks like a false positive.
Scan-build considers as possible to:
- have list_empty() return false;
- list_for_each_safe() to not execute any loop, thus not assigning
  a non-NULL value to 'block';
- the NULL pointer 'block' is passed to list_del().
This is not possible because with list_empty(), the loop runs at
least once.

Rewrite the function to simplify the code and making it easier for
scan-build to check it.

This also drops an incorrect use of list_for_each_safe(), where
the 'safe' version was not required.

Change-Id: Ia8b1d221cf9df73db1196e3f51986023dcaf78eb
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Fixes: 8d1dcf293a ("target/espressif: add application tracing functionality over JTAG")
Reviewed-on: https://review.openocd.org/c/openocd/+/7608
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Tested-by: jenkins

src/target/espressif/esp32_apptrace.c

@@ -356,18 +356,14 @@ static int esp32_apptrace_ready_block_put(struct esp32_apptrace_cmd_ctx *ctx, st
 
 static struct esp32_apptrace_block *esp32_apptrace_ready_block_get(struct esp32_apptrace_cmd_ctx *ctx)
 {
-	struct esp32_apptrace_block *block = NULL;
+	if (list_empty(&ctx->ready_trace_blocks))
+		return NULL;
 
-	if (!list_empty(&ctx->ready_trace_blocks)) {
-		struct list_head *head = &ctx->ready_trace_blocks;
-		struct list_head *tmp, *pos;
+	struct esp32_apptrace_block *block =
+		list_last_entry(&ctx->ready_trace_blocks, struct esp32_apptrace_block, node);
 
-		list_for_each_safe(pos, tmp, head) {
-			block = list_entry(pos, struct esp32_apptrace_block, node);
-		}
-		/* remove it from ready list */
-		list_del(&block->node);
-	}
+	/* remove it from ready list */
+	list_del(&block->node);
 
 	return block;
 }