NFC: implicitly deactivate in nci_start_poll

When start_poll is called, and a target was implicitly activated,
we need to implicitly deactivate it.
On the other hand, when the target was activated by the user,
we should not deactivate it.

Signed-off-by: Ilan Elias <ilane@ti.com>
Acked-by: Lauro Ramos Venancio <lauro.venancio@openbossa.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>