regulator: qcom_pm8008-regulator: correct chip-en chip variable type

Change the struct type of the "chip" variable in the chip-en
regulator callbacks from "struct pm8008_regulator *" to the
correct type: "struct pm8008_chip *".

Change-Id: I3f93ec629e791e4bc8da24222c005d681d168f82
Signed-off-by: David Collins <collinsd@codeaurora.org>