diag: Account for token offset while writing buffers to processors

While sending data to remote processors, the token is stripped off
from the buffer. Diag driver must account for this offset while
checking against the original buffer on write complete.

Change-Id: If2fffbafdcc5fcf2c037090fbb0e37bf0836971b
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>