Fix uart BK regs reading/writing

app/uart.c

@@ -446,7 +446,7 @@ static void CMD_0601_ReadBK4819Reg(const uint8_t *pBuffer)
 
 	struct __attribute__((__packed__)) {
 		Header_t header;
-		struct {
+		struct __attribute__((__packed__)) {
 			uint8_t reg;
 			uint16_t value;
 		} data;