selftests/powerpc: Remove the repeated declaration

Function 'event_ebb_init' and 'event_leader_ebb_init' are declared
twice in the header file, so remove the repeated declaration.

Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1622529385-5938-1-git-send-email-zhangshaokun@hisilicon.com