license.bbclass: fix license_create_manifest failed
While rpm incremental image generation enabled, invoked
license_create_manifest failed.
...
| ln: failed to create symbolic link 'tmp/work/qemux86_
64-poky-linux/core-image-base/1.0-r0/rootfs/usr/share/
common-licenses/alsa-conf-base/generic_GPLv2':File exists
| WARNING:tmp/work/qemux86_64-poky-linux/core-image-base/
1.0-r0/temp/run.license_create_manifest.26327:1 exit 1 from
| ln -s ../${lic}/home/jiahongxu/yocto/build-
20140120-
yocto-qemux86-64/tmp/work/qemux86_64-poky-linux/core-image
-base/1.0-r0/rootfs/usr/share/common-licenses/${pkg}/${lic}
...
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
