ARM: 9055/1: mailbox: arm_mhuv2: make remove callback return void

ARM: 9055/1: mailbox: arm_mhuv2: make remove callback return void

My build tests failed to catch that amba driver that would have needed
adaption in commit 3fd269e74f2f ("amba: Make the remove callback return
void"). Change the remove function to make the driver build again.

Link: https://lore.kernel.org/r/[email protected]
Reported-by: kernel test robot <[email protected]>
Fixes: 3fd269e74f2f ("amba: Make the remove callback return void")
Acked-by: Viresh Kumar <[email protected]>
Signed-off-by: Uwe Kleine-König <[email protected]>
Signed-off-by: Russell King <[email protected]>