core/deps.mk: Ensure $(ERLANG_MK_TMP) is created
core/deps.mk: Ensure $(ERLANG_MK_TMP) is created

... before writing to it.

This fixes the following error which is logged with a fresh checkout:
  /bin/sh: cannot create (...)/.erlang.mk/deps.log: No such file or directory

yannayl/erlang.mk,KrzysiekJ/erlang.mk,ninenines/erlang.mk,bsmr-erlang/erlang.mk,hairyhum/erlang.mk,rabbitmq/erlang.mk,a12n/erlang.mk,ingwinlu/erlang.mk,nevar/erlang.mk,jj1bdx/erlang.mk,crownedgrouse/erlang.mk