Audio default HAL: hidl_memory size must be positive

hidl_memory size is not used on the framework side but is checked by the
hidl framework to be a sensible value.
Due to a hack in O and P, the value can be negative, this leads to
errors in HIDL.

This patch make sure the hidl_memory size is always positive and thus
not affected by the hack.

Test: adb shell data/nativetest64/write_sine/write_sine -pl -m3 -x
Bug: 38118159
Change-Id: Ie53c46c558e8042d74ee32b55219195da82e4bcc
Signed-off-by: Kevin Rocard <krocard@google.com>