microblaze: Add missing double apostrophe in Kconfig

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index fd53e50..cd5837e 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -90,7 +90,7 @@
 
 menu "Processor type and features"
 
-source kernel/time/Kconfig
+source "kernel/time/Kconfig"
 
 source "kernel/Kconfig.preempt"