libion: save errno value

Ensure that the errno value is saved in ion_ioctl before calling ALOGE
in case ALOGE changes the errno which then changes the return value of
ion_ioctl.

Returning the wrong errno from ion_ioctl can be bad because it can cause
functions like ion_is_legacy to not behave properly.

Also apply the same fix to ion_map.

Change-Id: Ib994b465bfaccdf20963cfdc3f67d1cc5ff3cf8e