msm: adsprpc: do not free cached session buffers on power collapse

Avoid freeing the cached session buffers on power collapse as it
frees the other session context buffers.

Change-Id: If8f2fb1d9c63329e1a4635f7a56c3367c9d3004e
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>