OMAP: VP: Explicitly mask VPVOLTAGE field

Reading the VPVOLTAGE field of PRM_VP_*_VOLTAGE registers currently
relies on a u32 -> u8 conversion to mask off the FORCEUPDATEWAIT field
in the upper bits.  Make this explicit using the mask symbol
already defined, added as a new field in struct omap_vp_common.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>
diff --git a/arch/arm/mach-omap2/vp.c b/arch/arm/mach-omap2/vp.c
index e7d38f6..3807620 100644
--- a/arch/arm/mach-omap2/vp.c
+++ b/arch/arm/mach-omap2/vp.c
@@ -227,7 +227,8 @@
 		return 0;
 	}
 
-	curr_vsel = voltdm->read(vp->voltage);
+	curr_vsel = (voltdm->read(vp->voltage) & vp->common->vpvoltage_mask)
+		>> __ffs(vp->common->vpvoltage_mask);
 
 	if (!voltdm->pmic || !voltdm->pmic->vsel_to_uv) {
 		pr_warning("%s: PMIC function to convert vsel to voltage"