regulator: Update REGULATOR_EVENT_ENABLE mask value

REGULATOR_EVENT_PRE_VOLTAGE_CHANGE and REGULATOR_EVENT_ENABLE
currently share the same mask value resulting in a conflict.
Resolve this by using the largest 32-bit mask for
REGULATOR_EVENT_ENABLE to prevent future collisions.

Change-Id: I5aa25d2cebd12580db6a2bd69df68b7831619a75
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>