CP: Fix PD poll loop after the multi-drop-only change

Since we moved to the multi-drop-only approach, we cannot move on to
polling other PDs when one is still responding to a command. This patch
fixes a leak from the old implementation.

Signed-off-by: Siddharth Chandrasekaran <sidcha.dev@gmail.com>

Author: sidcha

src/osdp_cp.c

@@ -1630,6 +1630,15 @@ void osdp_cp_refresh(osdp_t *ctx)
 
 		state_update(pd);
 
+		/*
+		 * On a shared multi-drop bus the CP must complete one PD's
+		 * exchange before starting the next. Break while the channel
+		 * is occupied with a send/reply/retry cycle.
+		 */
+		if (cp_phy_running(pd)) {
+			break;
+		}
+
 		next_pd_idx = pd->idx + 1;
 		if (next_pd_idx >= cp_ctx->_num_pd) {
 			next_pd_idx = 0;