can: at91_can: add missing prepare and unprepare of the clock

can: at91_can: add missing prepare and unprepare of the clock

In order to make the driver work with the common clock framework, this patch
converts the clk_enable()/clk_disable() to
clk_prepare_enable()/clk_disable_unprepare(). While there, add the missing
error handling.

Signed-off-by: David Dueck <[email protected]>
Signed-off-by: Anthony Harivel <[email protected]>
Acked-by: Boris Brezillon <[email protected]>
Cc: linux-stable <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>