yocto-bsp: remove 'branch' statements in .scc if reusing branch

yocto-bsp: remove 'branch' statements in .scc if reusing branch

If reusing a branch (need_new_branch == 'n') we don't need to branch
in the .scc, so make it conditional on need_new_branch.

(From meta-yocto rev: 1e698ad2d18249c6224821bd52e3b979750db256)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>