megasas: remove unnecessary megasas_use_msi()

megasas overwrites user configuration when msi_init fail to flag internal msi
state, which is unsuitable. megasa_use_msi() is unnecessary, we can call
msi_uninit() directly when unrealize, even no need to call msi_enabled() first.

cc: Hannes Reinecke <hare@suse.de>
cc: Paolo Bonzini <pbonzini@redhat.com>
cc: Markus Armbruster <armbru@redhat.com>
cc: Marcel Apfelbaum <marcel@redhat.com>
cc: Michael S. Tsirkin <mst@redhat.com>

Acked-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
