coding style: remove useless return statement from void functions

coding style: remove useless return statement from void functions

For void functions, a return as last statement is useless.
Remove it.

Issue identified by checkpatch script from Linux kernel v5.1 using
the command

	find src/ -type f -exec ./tools/scripts/checkpatch.pl \
	-q --types RETURN_VOID -f {} \;

Change-Id: Ie0616fe98623f30d2d7b04ac9517d669774092de
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5622
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Tested-by: jenkins