[PATCH] splice: warning fix

From: Andrew Morton <akpm@osdl.org>

net/socket.c:148: warning: initialization from incompatible pointer type

extern declarations in .c files!  Bad boy.

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jens Axboe <axboe@suse.de>