msm: acpuclock-copper: Update use of regulator_get() for Krait core rails

Call regulator_get() with a device argument instead of NULL, and add
appropriate device-to-regulator mappings in the device tree and
board-copper-regulator.

This is necessary for regulator_get() to succeed when the real
regulator devices in the device tree are used instead of the stubs
currently in the board file.

Change-Id: I3697ed05e9ee3abd1521f58e3f883c00dd886f2f
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>