create-pull-request: fix git GIT_VERSION
If the git version is 1.7.9.5, then 1795 is bigger than 210 which causes
errors like:
fatal: No such ref: :rbt/bash
fatal: Needed a single revision
ERROR: git request-pull reported an error
Use the first 3 numbers to fix the problem.
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>