efi_selftest: fix use-after-free

efi_selftest: fix use-after-free

When the `memory' efi selftest verifies the Devicetree memory reservation,
it accesses the memory_map buffer after it has been freed with free_pool().
Move the verification earlier to fix this.

Fixes: 34c96659ed57 ("efi_selftest: check fdt is marked as runtime data")
Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>