diag: Set context properly while sending command responses

Currently, setting of context is not proper while sending
command responses due to which modem command response
buffer is getting corrupted leading to modem qshrink4
qdb file corruption. This patch fixes the issue by
setting the context properly.

CRs-Fixed: 2026664
Change-Id: I4bd2c23feaaf8a75a5a256d28377878519b507c6
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>