jtag: esp_usb_jtag: remove macro __packed

jtag: esp_usb_jtag: remove macro __packed

In FreeBSB 13.0 the build fails due to redefined macro __packed.

	src/jtag/drivers/esp_usb_jtag.c:19:9: error: '__packed' macro
	    redefined [-Werror,-Wmacro-redefined]
	#define __packed __attribute__((packed))
	        ^
	/usr/include/sys/cdefs.h:223:9: note: previous definition is here
	#define __packed        __attribute__((__packed__))
	        ^
	1 error generated.

Drop the macro and align the code with the other files in OpenOCD
project, where the attribute is directly applied without using a
macro.

Change-Id: I89ae943e77036206d40d4d54172cd4a73e76e5c5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reported-by: Wojciech Puchar <wojtek@puchar.net>
Reviewed-on: https://review.openocd.org/c/openocd/+/7435
Tested-by: jenkins
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>