diag: Fix to proper updation of buffering flag

This patch adressess the proper updation of
buffering flag with the check for streaming buffering
mode against the peripheral's buffering mode.

CRs-Fixed: 1017305
Change-Id: Idc4556e568a42aa2441295c9e3caa3f2c92c4cc6
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>