openocd: build: prevent old clone to fail on git submodules

openocd: build: prevent old clone to fail on git submodules

Working on an old local git repository, the git sub-modules could
have been set before last changes in .gitmodules.
The script 'bootstrap' does not update the url of the repositories
and this can cause the script to fail.

Add 'git submodule sync' to the script to update the url of the
repositories.
While there, fuse 'git submodule init' and git submodule update'
in a single command.

Reported-by: Karl Hammar <karl@aspodata.se>
Change-Id: I61412f804dbbb7a843aa009139ddb4b8e71beefb
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8375
Tested-by: jenkins