efi_selftest: block device: avoid read after free

Reading the position in a file after closing the same results in a read
after free.

Correct the sequence in the test.

Reported-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
1 file changed