clk: axm55xx: Use %zu in pr_info for size_t

Fix the following compiler warning:

drivers/clk/clk-axm5516.c: In function 'axmclk_probe':
drivers/clk/clk-axm5516.c:559:2: warning: format '%u' expects argument of type 'unsigned int', but argument 2 has type 'size_t' [-Wformat=]
  pr_info("axmclk: supporting %u clocks\n", num_clks);
    ^

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>