jtag: avoid checking for non NULL pointer to free it

jtag: avoid checking for non NULL pointer to free it

The function free() can be called with a NULL pointer as argument,
no need to check the argument before. If the pointer is NULL, no
operation is performed by free().

Remove the occurrences of pattern:
	if (ptr)
		free(ptr);

Change-Id: I2938e333bd1eac5218bd67aefb9d8f373da017a8
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5810
Tested-by: jenkins