ubi: fix UBI_SILENCE_MSG

 - drop CONFIG_ prefix from kconfig entry
 - fix small compilation issue with CONFIG_UBI_SILENCE_MSG

Signed-off-by: Markus Klotzbuecher <markus.klotzbuecher@kistler.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Cc: Kyungmin Park <kmpark@infradead.org>
diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 2b17eae..a78fd51 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -1,6 +1,6 @@
 menu "UBI support"
 
-config CONFIG_UBI_SILENCE_MSG
+config UBI_SILENCE_MSG
 	bool "UBI silence verbose messages"
 	default ENV_IS_IN_UBI
 	help