[crypto] Fix wrong setup in function aes_wrap

Use explicit size in memset because 8 bytes must be set always.

This problem was reported by cppcheck.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/crypto/aes_wrap.c

 	cipher_setkey ( &aes_algorithm, aes_ctx, kek, 16 );
 
 	/* Set up */
-	memset ( A, 0xA6, sizeof ( A ) );
+	memset ( A, 0xA6, 8 );
 	memmove ( dest + 8, src, nblk * 8 );
 
 	/* Wrap */