mei: amthif: drop READ_COMPLETE state

AMTHIF code now uses read completed queue to store replies from the FW.
It is possible to send the next request as soon as a read from the FW is
completed. With these changes we don't need the READ_COMPLETE state.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>