package_rpm: Don't check for the existence of dvar as its never used
If a sstate package exists for the package task but not for the rpm packaging
task, the output from the package task will be used. The directory pointed
to by dvar will not exist under this scenario.
Since the directory is never used by the packaging process remove the
check, substituting the pkgd variable which is always present and used.
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>
