msm: pm: avoid array overrun for msm_pm_sleep_modes

The array is not defined for the maximum possible size.
So it is possible that the array may overrun when it is
dereferenced using MSM_PM_MODE macro.

Add a dummy entry to make sure array is of max size.

Change-Id: I5783b0aa6c8295c5c5aabcb498700c6af1a3eba5
Signed-off-by: Venkat Devarasetty <vdevaras@codeaurora.org>