staging: slicoss: Use inplace convert with __be32 *

This patch fixes "cast to restricted __be32"
sparse warning.

remove  temporary value assignment and use inplace
__be32 conversion for ntohl function which is can
get big endian format

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>