msm: ADSPRPC: unmap fd failure to find map

Handle error returned from finding map by fd and unmap.

Change-Id: If5515f1a292c468c87481a2917642c920c43652b
Acked-by: Viswanatham Paduchuri <vpaduchu@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>