license.bbclass: set dirs for do_populate_lic_setscene

Fixed:
ERROR: Build of do_populate_lic failed
ERROR: Traceback (most recent call last):
  File "bitbake/lib/bb/build.py", line 497, in exec_task
    return _exec_task(fn, task, d, quieterr)
  File "bitbake/lib/bb/build.py", line 437, in _exec_task
    exec_func(func, localdata)
  File "bitbake/lib/bb/build.py", line 212, in exec_func
    exec_func_python(func, d, runfile, cwd=adir)
  File "/home/nxadm/nx/ala-blade44.1/builds-2015-03-09-163005/qemuppc_world_oe_bp/bitbake/lib/bb/build.py", line 237, in exec_func_python
    os.chdir(cwd)
OSError: [Errno 2] No such file or directory: 'bitbake_build/tmp/work/ppc7400-wrs-linux/taglib/1.9.1-r0/build'

When running setscene, the cwd is $B which maybe removed by
autotools.bbclass or cmake.bbclass when rebuild.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Armin Kuster <akuster@smtp.gmail.com>