drivers: cpuidle: lpm-levels: Fix untrusted pointer dereference.

The list_for_each macro was not used correctly, where the intermediate
variable would be LIST_POISON, resulting in a untrusted pointer
dereference. Switch to using list_for_each_entry_safe to for safe
removal of a list entry.

Change-Id: I0e0fd5dd9f251b5093d6e9d6335387512ec59249
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>