vmm: Collapse identical case statements in vlapic_icrlo_write_handler()

No functional change intended.

Reviewed by: jhb, corvink
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D38446

(cherry picked from commit f3bbd0e818008ddc4fbf1f6ade0f7e411b1dfee5)