sha512_224: Fix SHA512_224_Final() on little-endian machines.
PR: 266863
MFC after: 1 week
Reviewed by: allanjude, cperciva, des
Differential Revision: https://reviews.freebsd.org/D38372
(cherry picked from commit 6680cfe8e0eec4427716ab50d73ab8231dd9ab28)