clk: vt8500: Missing breaks in vtwm_pll_round_rate/_set_rate.

The case of PLL_TYPE_WM8750 in both these functions is missing a break
statement causing a fall-through to the default: case.

Insert the missing break statements.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Mike Turquette <mturquette@linaro.org>