trace: Fix incorrect megasas trace parameters

hw/scsi/trace-events lists cmd as the first parameter for both
megasas_iovec_overflow and megasas_iovec_underflow, but the caller
was mistakenly passing cmd->iov_size twice instead of the command
index.  Also, trace_megasas_abort_invalid is called with parameters
in the wrong order.  Broken since its introduction in commit
e8f943c3.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>