iwlwifi: mvm: fix non-ACPI function

The code now compiles without ACPI, but there's a warning since
iwl_mvm_get_ppag_table() isn't used, and iwl_mvm_ppag_init() must
not unconditionally fail but return success instead.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>