dmaengine: sdxi: context: Document omitted default in switch stmt

See https://lore.kernel.org/dmaengine/20250917143410.00005bb4@huawei.com/

Add a break though.

Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>

Author: nathanlynch

drivers/dma/sdxi/context.c

@@ -289,6 +289,8 @@ static const char *cxt_sts_state_str(enum cxt_sts_state state)
 	case CXTV_STOPG_FN:
 	case CXTV_ERR_FN:
 		str = context_states[state];
+		break;
+	/* default: label deliberately omitted so -Wswitch will work. */
 	}
 
 	return str;