userspace: eliminate warning in process_gperf.py

Python 3.7 throws a FutureWarning when it thinks it
has found a nested set in a regular expression.

We weren't actually; just trying to match some brackets.
Escape them instead. No functional difference.

Fixes: #11961

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
1 file changed