clk: vt8500: Use common of_clk_init() function

Use common of_clk_init() function for clock initialization.

Signed-off-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Tested-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: added entry for wm8750-pll-clock]

Signed-off-by: Mike Turquette <mturquette@linaro.org>