can: at91_can: Fix memory leak in at91_can_probe()

can: at91_can: Fix memory leak in at91_can_probe()

In at91_can_probe(), the dev structure is allocated via alloc_candev().
However, if the subsequent call to devm_phy_optional_get() fails, the
code jumps directly to exit_iounmap, missing the call to free_candev().
This results in a memory leak of the allocated net_device structure.

Fix this by jumping to the exit_free label instead, which ensures that
free_candev() is called to properly release the memory.

Compile tested only. Issue found using a prototype static analysis tool
and code review.

Fixes: 3ecc09856afb ("can: at91_can: add CAN transceiver support")
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
Link: https://patch.msgid.link/20260122114128.643752-1-zilin@seu.edu.cn
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>