Remove extra memset() left after r342388.

This memset() wiped MPI2_FUNCTION_SCSI_TASK_MGMT set by mprsas_alloc_tm(),
that broke target reset on device removal, making later re-insertion into
the same slot impossible, since firmware was still waiting for the driver
to finish with the removed device.

MFC after: 1 week
Sponsored by: iXsystems, Inc.