diag: Copy limited data from and to the user space

Diag clients can issue IOCTLs to get the next delayed response
id from the Diag driver. This patch removes unnecessary data
being copied from and to the user space.

Change-Id: I13cf17252d2a85b999fd4645714ee1d8143e5ccc
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>