ASoC: wm9081: Fix setting soft VMID ramp enable with VMID 2*240k

According to the datasheet:
BIT 2:1
        VMID_SEL[1:0] VMID Divider Enable and Select
        00 = VMID disabled
        01 = 2x40k Omh divider
        10 = 2x240k Omh divider
        11 = 2x5k Omh divider

To set VMID 2*240k, we should OR reg with 0x04 instead of 0x40.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>