ARM: debug: fix wording error in DEBUG_LL_UART_NONE option help

The DEBUG_LL_UART_NONE option was moved from the top of the list to
the bottom - unfortunately, it still referred to the options "below"
rather than "above".
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/Kconfig.debug

@@ -579,7 +579,7 @@ choice
 		depends on !ARCH_MULTIPLATFORM
 		help
 		  Say Y here if your platform doesn't provide a UART option
-		  below. This relies on your platform choosing the right UART
+		  above. This relies on your platform choosing the right UART
 		  definition internally in order for low-level debugging to
 		  work.