can: m_can: Fix runtime resume call

pm_runtime_get_sync() returns a 1 if the state of the device is already
'active'. This is not a failure case and should return a success.

Therefore fix error handling for pm_runtime_get_sync() call such that
it returns success when the value is 1.

Also cleanup the TODO for using runtime PM for sleep mode as that is
implemented.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Cc: <stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>