sys/compat/freebsd32: Fix i386 compilation

The compile assertion now failing is due to the change 'int64_t' =>
'int32_t' as the type of 'time32_t' on i386, which is the correct
value. The use of 'freebsd32.h' on i386 may seem strange, but it comes
from 'kern_umtx.c' including it unconditionally as it needs 'struct
umutex32'.

Fixes: 87632ddf67b0 ("openzfs sys/types32.h: use abi_compat.h for time32_t")
Sponsored by: The FreeBSD Foundation