PEL: Remove use of deprecated mem_fun
PEL: Remove use of deprecated mem_fun

Replace it with mem_fn.

Signed-off-by: Matt Spinler <c000c989d08c98662d98f15448f11de169feb92d@us.ibm.com>
Change-Id: I1b223f2de54f9b6c6883fb539276f9750575ab96

openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging