Update src/naming.adoc

Signed-off-by: Kersten Richter <[email protected]>

Author: kersten1

src/naming.adoc

@@ -78,7 +78,7 @@ of the P extension.
 
 Standard unprivileged extensions can also be named by using a single "Z" followed by an
 alphanumeric name. The name must end with an alphabetical character or an 
-optional version number. The second letter from the bottom cannot be a numeric if the
+optional version number. The second letter from the end cannot be numeric if the
 last letter is ``p''. For example, "Zifencei" names the instruction-fetch fence extension
 described in <<zifencei>>; "Zifencei2" and "Zifencei2p0" name version 2.0 are the same.