regulator: vctrl: Fix out of bounds array access for vctrl->vtable

Current code only allocates rdesc->n_voltages entries for vctrl->vtable.
Thus use rdesc->n_voltages instead of n_voltages in the for loop.

While at it, also switch to use devm_kcalloc instead of devm_kmalloc_array
+ __GFP_ZERO flag and fix the argument order.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>