[qca-nss-ecm] Fix invalid pointer typecast for callback_t in msg_init APIs

msg_init() APIs don't need a typecast for callbacks. Fix the invalid typecast
for all the callbacks in msg_init.

Change-Id: Icf14fc73cc4d9247333c00efaf22cc55e1c60946
Signed-off-by: Sundarajan Srinivasan <sundaraj@codeaurora.org>
2 files changed