efi/efi_test: Use memdup_user() as a cleanup

Fix coccicheck warning which recommends to use memdup_user().

This patch fixes the following coccicheck warnings:

  drivers/firmware/efi/test/efi_test.c:269:8-15: WARNING opportunity for memdup_user

Signed-off-by: Ivan Hu <ivan.hu@canonical.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20161018143318.15673-7-matt@codeblueprint.co.uk


Signed-off-by: Ingo Molnar <mingo@kernel.org>