efivar: fix import functionality

"efivar --import" is broken in v38:

 # efivar -i /8be4df61-93ca-11d2-aa0d-00e098032b8c-Timeout
free(): invalid pointer
Aborted

Backport upstream patch to fix it.

Upstream issue:
https://github.com/rhboot/efivar/issues/173



Signed-off-by: Grygorii Tertychnyi <grygorii.tertychnyi@leica-geosystems.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>