can: gw: use call_rcu() instead of costly synchronize_rcu()

can: gw: use call_rcu() instead of costly synchronize_rcu()

Commit fb8696ab14ad ("can: gw: synchronize rcu operations
before removing gw job entry") added three synchronize_rcu() calls
to make sure one rcu grace period was observed before freeing
a "struct cgw_job" (which are tiny objects).

This should be converted to call_rcu() to avoid adding delays
in device / network dismantles.

Use the rcu_head that was already in struct cgw_job,
not yet used.

Link: https://lore.kernel.org/all/[email protected]
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Oliver Hartkopp <[email protected]>
Tested-by: Oliver Hartkopp <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>