MIPS: sni: Remove the read_persistent_clock()

The dummy read_persistent_clock() uses a timespec, which is not year
2038 safe on 32bit systems. Thus remove this obsolete interface.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/19114/


Signed-off-by: James Hogan <jhogan@kernel.org>