Add quotation marks around $PATH for deb-utils

Fix #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 #14339