Update platform-common submodule (sonic-net#5261)

Updating platform-common submodule with these commits

commit 14c6e53 
    [sff8472.py] Make hex keys all lowercase (sonic-net#115)
    Alpha chars in hex-based keys should be lowercase

commit b60f46c
    Sfputil base and helper class changes for multi-ASIC (sonic-net#100)
    * Sfputil base and helper class changes for multi-ASIC
          > adding the logical interface to asic id mapping
    * Updated based on new sonic-py-common API's.