Git rev-list --max-count needs an = for assignment

* install_modules.sh: When invoking git rev-list with --max-count it
only supports = and not space before the value. The previous
implementation was flawed and only ever resulted in git errors about
an unrecognized ref for which it was misinterpreting the --max-count
value as representing.

Change-Id: I11f8f5b6e13d4640d6558f423292ad7e7b89961f
Merge "Git rev-list --max-count needs an = for assignment"