getrusage(2): fix return value under 32-bit emulation

According to the man page, getrusage(2) should return EFAULT if the rusage
argument lies outside of the process's address space. But due to an
oversight in r100384, that's never been the case during 32-bit emulation.
Fix it.

PR: 230153
Reported by: tests(7)
Reviewed by: cem
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D16500