CMSIS-NN: Fix warning in arm_nnsupportfunctions.h
CMSIS-NN: Fix warning in arm_nnsupportfunctions.h

Warnings related to sign conversions are looked at
and typecasted.

Change-Id: I1842c88054472e2aea659acf7c61cb2f31e28ecf

ARM-software/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5