m68knommu: improve short help of m68knommu/Kconfig/RAMSIZE for '0' case

While it is explained in the long help text, meaning of '0' for RAMSIZE
is easily overlooked because is not mentioned in the short help text.
Add that.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
diff --git a/arch/m68knommu/Kconfig b/arch/m68knommu/Kconfig
index 064f591..efeb603 100644
--- a/arch/m68knommu/Kconfig
+++ b/arch/m68knommu/Kconfig
@@ -566,7 +566,7 @@
 	  processor address space.
 
 config RAMSIZE
-	hex "Size of RAM (in bytes)"
+	hex "Size of RAM (in bytes), or 0 for automatic"
 	default "0x400000"
 	help
 	  Define the size of the system RAM. If you select 0 then the