HAL in_get_parameters: do not return unknown keys

out_get_parameters and adv_get_parameters only return keys that are
supported. That allows the client the discriminate between keys not
supported and empty return value.

in_get_parameters used to have this behaviour too until it was broken by
I4f4142aba495e9625b17ba007280f76fbc66a641.

This patch restores the original in_get_parameters behaviour.

Test: vts-tradefed run vts --module VtsHalAudioV2_0Target
Bug: b/63801053
Change-Id: I8888f61f0b908aaa436577729a2c9d8b35955b6d
Signed-off-by: Kevin Rocard <krocard@google.com>