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

drivers/firmware/efi/test/efi_test.c

@@ -265,14 +265,10 @@ static long efi_runtime_set_variable(unsigned long arg)
 			return rv;
 	}
 
-	data = kmalloc(setvariable.data_size, GFP_KERNEL);
-	if (!data) {
+	data = memdup_user(setvariable.data, setvariable.data_size);
+	if (IS_ERR(data)) {
 		kfree(name);
-		return -ENOMEM;
-	}
-	if (copy_from_user(data, setvariable.data, setvariable.data_size)) {
-		rv = -EFAULT;
-		goto out;
+		return PTR_ERR(data);
 	}
 
 	status = efi.set_variable(name, &vendor_guid,