Kconfig: lib/Kconfig.ubsan fix reference to ubsan documentation

Documenation/ubsan.txt was moved to Documentation/dev-tools/ubsan.rst,
this fixes the reference.

Link: http://lkml.kernel.org/r/1476698152-29340-3-git-send-email-andreas.platschek@opentech.at
Signed-off-by: Andreas Platschek <andreas.platschek@opentech.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.ubsan

@@ -10,7 +10,8 @@ config UBSAN
 	  This option enables undefined behaviour sanity checker
 	  Compile-time instrumentation is used to detect various undefined
 	  behaviours in runtime. Various types of checks may be enabled
-	  via boot parameter ubsan_handle (see: Documentation/ubsan.txt).
+	  via boot parameter ubsan_handle
+	  (see: Documentation/dev-tools/ubsan.rst).
 
 config UBSAN_SANITIZE_ALL
 	bool "Enable instrumentation for the entire kernel"