clk: zte: Mark pll config tables as const

These should be const.

Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>