regulator: s5m8767: Fix to read the first DVS register.

This patch modifies the DVS register read function to select correct DVS1
register. This change is required because the GPIO select pin is 000 in
unintialized state and hence selects the DVS1 register.

Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>