Fix gcc unused value warnings in FreeBSD zfs_prop.c

[dim]

Summary

With gcc we are seeing the following -Werror warnings:

/workspace/src/sys/contrib/openzfs/include/os/freebsd/spl/sys/simd.h:53:33: error: statement with no effect [-Werror=unused-value]
   53 | #define simd_stat_init()        0
      |                                 ^
/workspace/src/sys/contrib/openzfs/module/zcommon/zfs_prop.c:1092:9: note: in expansion of macro 'simd_stat_init'
 1092 |         simd_stat_init();
      |         ^~~~~~~~~~~~~~
/workspace/src/sys/contrib/openzfs/module/zcommon/zfs_prop.c: In function 'zcommon_fini':
/workspace/src/sys/contrib/openzfs/include/os/freebsd/spl/sys/simd.h:54:33: error: statement with no effect [-Werror=unused-value]
   54 | #define simd_stat_fini()        0
      |                                 ^
/workspace/src/sys/contrib/openzfs/module/zcommon/zfs_prop.c:1100:9: note: in expansion of macro 'simd_stat_fini'
 1100 |         simd_stat_fini();
      |         ^~~~~~~~~~~~~~

Both simd_stat_init() and simd_stat_fini() are defined in the FreeBSD
specific version of simd.h:

#define	simd_stat_init()	0
#define	simd_stat_fini()	0

These should both be defined as do {} while (0)" instead, similar to
other macros in this file.