Commit branch: fix user param key
Commit branch: fix user param key

Commit branch was taken from 'git_commit' instead of 'git_branch' user
param.

* OSBS-6599

Signed-off-by: Martin Bašti <388356a3851efe39ff0604de6d8fb2e16e10a0b7@redhat.com>

projectatomic/atomic-reactor,DBuildService/atomic-reactor,projectatomic/atomic-reactor,fr34k8/atomic-reactor,fr34k8/atomic-reactor,DBuildService/atomic-reactor