RSA: Don't select non-existent symbol

You can select MPILIB_EXTRA all you want, it doesn't exist ;-)

Surprised kconfig doesn't complain about that...
Signed-off-by: NJean Delvare <jdelvare@suse.de>
Acked-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>

crypto/asymmetric_keys/Kconfig

@@ -22,7 +22,6 @@ config ASYMMETRIC_PUBLIC_KEY_SUBTYPE
 
 config PUBLIC_KEY_ALGO_RSA
 	tristate "RSA public-key algorithm"
-	select MPILIB_EXTRA
 	select MPILIB
 	help
 	  This option enables support for the RSA algorithm (PKCS#1, RFC3447).