clk: at91: fix pmc_clk_ids data type attriubte

Fix pmc_clk_ids data type attribute (__initdata -> __initconst).

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>