IB/hfi1: Remove the repeated declaration

Function 'init_credit_return' and 'sc_return_credits' are declared twice,
remove the repeated declaration.

Link: https://lore.kernel.org/r/1621417415-3772-1-git-send-email-zhangshaokun@hisilicon.com


Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>