lg2: fix clang issue on nullptr_t
lg2: fix clang issue on nullptr_t

clang-tidy is more pedantic that nullptr_t is actually in std and
fails unless it is specified as such.

Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>
Change-Id: I74aa5a5af17fd5d4610fed4707564576c6ac22f1

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