clk: imx: clk-imx7ulp: Add missing sentinel of ulp_div_table

There should be a sentinel of ulp_div_table, otherwise _get_table_div
may access data out of the array.

Fixes: b1260067

 ("clk: imx: add imx7ulp clk driver")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>