Add quotation marks around $PATH for deb-utils

Fix openzfs#14338, failing to build deb-utils if existing `$PATH` variable
would include a whitespace.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Martin Rüegg <martin.rueegg@metaworx.ch>
Closes openzfs#14339

config/deb.am

@@ -74,7 +74,7 @@ deb-utils: deb-local rpm-utils-initramfs
 ## Debianized packages from the auto-generated dependencies of the new debs,
 ## which should NOT be mixed with the alien-generated debs created here
 	chmod +x $${path_prepend}/dh_shlibdeps; \
-	env PATH=$${path_prepend}:$${PATH} \
+	env "PATH=$${path_prepend}:$${PATH}" \
 	fakeroot $(ALIEN) --bump=0 --scripts --to-deb --target=$$debarch \
 	    $$pkg1 $$pkg2 $$pkg3 $$pkg4 $$pkg5 $$pkg6 $$pkg7 \
 	    $$pkg8 $$pkg9 $$pkg10 || exit 1; \