redhat/Makefile: Fix dist-brew and distg-brew targets

The dist-brew and distg-brew targets are failing because of a coding
error; make variables can only be specified one per line.

Additional fix request: Move --scratch to command from BUILD_TARGET
variable.

Fix dist-brew and distg-brew targets by breaking the variable assignments
into separate lines.

Successful build with these changes:
https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=46222147

Signed-off-by: Prarit Bhargava prarit@redhat.com