lib: digital signature config option name change

It was reported that DIGSIG is confusing name for digital signature
module. It was suggested to rename DIGSIG to SIGNATURE.

Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index 201e1b3..854735d 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -302,7 +302,7 @@
 	  This code in unnecessary for RSA digital signature verification,
 	  and can be compiled if needed.
 
-config DIGSIG
+config SIGNATURE
 	tristate "In-kernel signature checker"
 	depends on KEYS
 	select MPILIB