vts: VtsHalGraphicsMapperV2_1TargetTest fixup's

1) handles allocated through 'allocate' should be removed through
   'freeBuffer'.

2) make use of intended buffer handle in GetTransportSizeBadBuffer.

Bug: 146444563
Test: build, boot, VtsHalGraphicsMapperV2_1TargetTest

Cherry pick to master from android10-tests-dev

Change-Id: I6c1a67fc36dbc653ec2ada6a335d685d21e82800
Merged-In: I6c1a67fc36dbc653ec2ada6a335d685d21e82800
Signed-off-by: Pierre Couillaud <pierre.couillaud@broadcom.com>