ntb: ntb_pingpong: remove redundant initialization of variables msg_data and spad_data

The variables msg_data and spad_data are being initialized with values
that are never read, they are being updated later on. The initializations
are redundant and can be removed.

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