drivers: lpm-levels: Return correct value while suspend

Currently lpm_suspend_enter and lpm_cpuidle_s2idle return
success always. This misleads on succcess and failure counts.

This change adds support to return correct value to caller.

Change-Id: I57dd0a4385f16f0e0aa1c92d602c0816ed358e2c
Signed-off-by: Tushar Nimkar <tnimkar@codeaurora.org>