Correct test data size in keystore signing and verification tests.

The test is sending too much data to be signed, which should actually
fail, and does on Volantis.  Apparently the other keymaster implementors
do something to pass it, because shamu and hammerhead pass, but the test
is wrong.

Change-Id: Ic616a551567d64f5d87d9607ceb08afa7be74f9d