regulator: ab8500: Remove unused embedded struct expand_register

Used primarily for the AB8540 which lost support in early 2018.
It is now deemed safe to remove this legacy data structure.

Also fixes W=1 issue:

  drivers/regulator/ab8500.c:88: warning: Function parameter or member 'expand_register' not described in 'ab8500_regulator_info'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200625163614.4001403-6-lee.jones@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/ab8500.c

@@ -59,6 +59,7 @@ struct ab8500_shared_mode {
  * @voltage_bank: bank to control regulator voltage
  * @voltage_reg: register to control regulator voltage
  * @voltage_mask: mask to control regulator voltage
+ * @expand_register: 
  */
 struct ab8500_regulator_info {
 	struct device		*dev;
@@ -79,12 +80,6 @@ struct ab8500_regulator_info {
 	u8 voltage_bank;
 	u8 voltage_reg;
 	u8 voltage_mask;
-	struct {
-		u8 voltage_limit;
-		u8 voltage_bank;
-		u8 voltage_reg;
-		u8 voltage_mask;
-	} expand_register;
 };
 
 /* voltage tables for the vauxn/vintcore supplies */