NTB: ntb_transport: remove redundant assignment to rc

Variable rc is initialized to a value that is never read and it
is re-assigned later. The initialization is redundant and can be
removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>