spl: sdp: Detach the controller on error

In case anything errors out during the SDP transfer, detach
the controller instead of bailing out right away. This way,
the controller can be reattached on next attempt.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Marek Vasut <marex@denx.de>