jtag: fix build with configure --enable-verbose

jtag: fix build with configure --enable-verbose

With flag --enable-verbose, configure enables compiling some
conditional code that with new gcc triggers an error:
	error: '%04x' directive output may be truncated writing
	between 4 and 8 bytes into a region of size 5
	[-Werror=format-truncation=]

Extend the buffer to contain the full 8 bytes of %04x on a 'int'
and change the limit in snprintf.
Skip the intermediate buffer 's[4]'.
Align the code to the coding style.

Change-Id: Ifc8a6e4686555578a7355a1f6049471fd5e31913
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reported-by: Karl Hammar <karl@aspodata.se>
Reported-by: Tommy Murphy <tommy_murphy@hotmail.com>
Fixes: https://sourceforge.net/p/openocd/tickets/376/
Reviewed-on: https://review.openocd.org/c/openocd/+/7403
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>