crypto: virtio - don't use 'default m'

Drivers shouldn't be enabled by default unless there is a very good
reason to do so.  There doesn't seem to be any such reason for the
virtio crypto driver, so change it to the default of 'n'.
Signed-off-by: Ram Muthiah <rammuthiah@google.com>
[EB: adjusted commit message]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/virtio/Kconfig

@@ -5,7 +5,6 @@ config CRYPTO_DEV_VIRTIO
 	select CRYPTO_AEAD
 	select CRYPTO_SKCIPHER
 	select CRYPTO_ENGINE
-	default m
 	help
 	  This driver provides support for virtio crypto device. If you
 	  choose 'M' here, this module will be called virtio_crypto.