oe/package: enhance objdump command call with llvm

oe/package: enhance objdump command call with llvm

Replace `${HOST_PREFIX}objdump` with `${OBJDUMP}`.

When utilizing llvm for compiling packages, the invocation of GNU objdump
will consistently occur during package precess. This behavior is unfriendly
to llvm. So prefer `${OBJDUMP}` over `${HOST_PREFIX}objdump`.

Signed-off-by: lixiaoyong <lixiaoyong19@huawei.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>