package: fix dependency generation

A bug in release/packages/generate-ucl.sh causes package dependencies
(other than shlib depends) to not be generated correctly, meaning
packages are missing their dependencies.

generate-ucl.sh creates the UCL file by:

1. copying ${uclsource} (template.ucl) to ${uclfile}
2. appending dependencies to ${uclfile}
3. calling generate-ucl.lua on ${uclsource} to create ${uclfile}

This breaks because the dependencies added in step 2 are overwritten in
step 3.

Fix this by calling generate-ucl.lua with ${uclfile} as both the input
and output file, so anything we added to ${uclfile} is preserved.

PR: 286551
Reviewed by: des, imp
Approved by: re (cperciva)
Approved by: kevans (mentor, stable/14 mfc)
Pull Request: https://github.com/freebsd/freebsd-src/pull/1203

(cherry picked from commit e05b6502f9ca36860236644884f12eff8e3243c4)
(cherry picked from commit fb6b1a797349992d8f166a2724eab2caf59abe28)