clang: Fix include path for pldm_utils.hpp

Updated the include directive in pldm_oem_cmds.cpp to correctly
reference the path to pldm_utils.hpp. This resolves the issue
fixes the error below

'''
host-transport-extensions/pldm/oem/ibm/pldm_oem_cmds.cpp:19:10:
  error: 'pldm_utils.hpp' file not found [clang-diagnostic-error]
'''

Change-Id: I34a99d1ba199be045da63e92d896ded100865ba7
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>