MIPS: Remove declaration of obsolete arch_init_clk_ops()

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Cc: Apelete Seketeli <apelete@seketeli.net>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7671/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>