defconfig: lahaina-gki: disable the fixed regulator driver

Remove CONFIG_REGULATOR_FIXED_VOLTAGE=m from lahaina_GKI.config
since CONFIG_REGULATOR_FIXED_VOLTAGE=y is present in gki_defconfig.
The config entry in lahaina_GKI.config results in fixed.ko being
compiled.  However, it fails to load at runtime since the
statically compiled version of the fixed regulator driver is
already loaded along with the GKI base kernel image.

Change-Id: I561d642f98d42d924baca20ec91717f64946041d
Signed-off-by: David Collins <collinsd@codeaurora.org>