PCI: aerdrv: rework get_e_source()

Current get_e_source() returns pointer to an element of array.
However since it also progress consume counter, it is possible
that the element is overwritten by newly produced data before
the element is really consumed.

This patch changes get_e_source() to copy contents of the element
to address pointed by its caller.  Once copied the element in
array can be consumed.

And relocate this function to more innocuous place.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>