msm: adsprpc: return proper error code while getting device info

Return a different error code when a non-secure fastrpc device
node has been configured as a secure channel to avoid conflicts
with other failures. Set virtual address of remote buffers to
NULL before mapping them on DSP.

Change-Id: I8b3547e2dabd88b70d69ab0cb6b35514fc697936
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>