misc: fastrpc: Unmap only if buffer is unmapped from DSP

For unmapping any buffer from kernel, it should first be unmapped
from DSP. In case unmap from DSP request fails, the map should not
be removed from kernel as it might lead to SMMU faults and other
memory issues.

Fixes: 5c1b97c7

 ("misc: fastrpc: add support for FASTRPC_IOCTL_MEM_MAP/UNMAP")
Cc: stable <stable@kernel.org>
Signed-off-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20231013122007.174464-5-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>