lib: rsa: fix dependency for SPL_RSA_VERIFY

SPL_RSA_VERIFY requires SPL_RSA to be enabled. Add correct
dependency.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
index a90d67e..cf802a6 100644
--- a/lib/rsa/Kconfig
+++ b/lib/rsa/Kconfig
@@ -20,6 +20,7 @@
 
 config SPL_RSA_VERIFY
 	bool
+	depends on SPL_RSA
 	help
 	  Add RSA signature verification support in SPL.