hla_target: fix adapter_poll() to preserve TARGET_DEBUG_RUNNING state

Without this change TARGET_DEBUG_RUNNING changes to TARGET_RUNNING
after adapter_poll()

Change-Id: I1c965a43527b50fa723d78fb6eae56585a7ede03
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/4820
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/hla_target.c

@@ -470,6 +470,9 @@ static int adapter_poll(struct target *target)
 	if (prev_target_state == state)
 		return ERROR_OK;
 
+	if (prev_target_state == TARGET_DEBUG_RUNNING && state == TARGET_RUNNING)
+		return ERROR_OK;
+
 	target->state = state;
 
 	if (state == TARGET_HALTED) {