fix(cpufeat): update FEAT_PAUTH's feat detect line to tri-state

Since patch 8d9f5f258, FEAT_PAUTH has supported the tri-state framework.
This part was missed, update it.

Change-Id: I3e086865df4d852e9d31a04cd8150d9d8a4dd2b8
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
1 file changed