Clean up null pointer asserts by returning the error status to the
caller in the below spectral module files
1.spectral/core/spectral_common.c
2.target_if/spectral/target_if_spectral.h
3.target_if/spectral/target_if_spectral.c
Change-Id: Ib8d49c06928379768fb41e34d721bd3840e86330
CRs-Fixed: 3587512