x86: Fix a typo: segment fix -> segment prefix.

Author: bsdjhb

chap-cheri-x86-64.tex

@@ -401,7 +401,7 @@ \subsubsection{Addresses Relative to CFS and CGS}
 respectively.
 
 Other segment prefixes are not permitted in capability-aware
-addressing.  Attempting to use a segment fix other than \FS{} or
+addressing.  Attempting to use a segment prefix other than \FS{} or
 \GS{} with a capability-aware address should raise an illegal
 instruction exception.