The loop which checks to see if "dynamic" IDT entries are allocated
needs to compare with the trampoline address of the reserved ISR.
Otherwise it will never succeed.

Reported by:	Harry Schmalzbauer <freebsd@omnilan.de>
Tested by:	Harry Schmalzbauer <freebsd@omnilan.de>
Reviewed by:	kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D30576