meta/lib/oe/sbom30.py: correct alias

meta/lib/oe/sbom30.py: correct alias

After commit [spdx 3.0: Rework how SPDX aliases are linked] applied,
it added extra "/" to namespace, which causing the replacement of
UNIHASH missing a "/"

  http://spdxdocs.org/openembedded-alias/by-doc-hash/0b308e4b9ad979f642d8787c61f76c31bdcad04837eeaaf8bc383f33f99bbeb8/flex-nativeUNIHASH/build/recipe

After applying this commit to remove "/" from namespace.

  http://spdxdocs.org/openembedded-alias/by-doc-hash/0b308e4b9ad979f642d8787c61f76c31bdcad04837eeaaf8bc383f33f99bbeb8/flex-native/UNIHASH/build/recipe

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>