staging: android: ion: Get rid of ion_reserve

ion_reserve was supposed to be used to reserve memory in board files.
These days, board files are no more and there are other more controlled
mechanisms for reserving memory. Get rid of this function.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>