Make efivar-dp.h inlines compatible with --std=c89

Make efivar-dp.h inlines compatible with --std=c89

Some people still insist on compiling programs with a C standard from
the beginning of time, and that doesn't allow mixed declarations and
code.

We don't heavily depend on that, so this just fixes up the places where
we use it.

Fixes issue #54

Signed-off-by: Peter Jones <pjones@redhat.com>