package/environment-setup: Fix incorrect order of the `sed` expressions

package/environment-setup: Fix incorrect order of the `sed` expressions

Order of the `sed` expressions is important; when this was commited
to master, the order of the expressions from the original patch [1] was
changed, rendering the second expression to noop.

This made all the environment variables from the script to contain
absolute paths: long absolute paths makes verbose builds difficult
to read/follow.
We can take advantage of the fact that the PATH is updated and we
don't have to use absolute paths.

Fixed by reordering the `sed` expresions:
* first update the path of the binaries: e.g. 's%$(HOST_DIR)/bin/%%g'
* only then update remaining paths: e.g. 's%$(HOST_DIR)%\$$SDK_PATH%g'

[1] https://patchwork.ozlabs.org/project/buildroot/patch/20201027140140.47982-1-matthew.weber@rockwellcollins.com/

Signed-off-by: Mircea GLIGA <mgliga@bitdefender.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>