BTA HF CLIENT: Unset initial SCO value

Initialize the block with invalid SCO state so that while allocating the
if condition does not ignore the block. This was causing the stack to
not initiate a SCO connection to the remote (AG role)

Bug: b/33555377
Test: Check for SCO initialied on audio call
Change-Id: I3f5619c69288483bfa45c2a1adcf22008e353841