Update register-usage.md

Callee cannot tell if it is needed or not.

Author: hikaru-i

docs/build/register-usage.md

@@ -56,8 +56,8 @@ The [!INCLUDE[vcprx64](../assembler/inline/includes/vcprx64_md.md)] architecture
 |XMM3, YMM3|Volatile|Fourth FP argument; fourth vector-type argument when `__vectorcall` is used|  
 |XMM4, YMM4|Volatile|Must be preserved as needed by caller; fifth vector-type argument when `__vectorcall` is used|  
 |XMM5, YMM5|Volatile|Must be preserved as needed by caller; sixth vector-type argument when `__vectorcall` is used|  
-|XMM6:XMM15, YMM6:YMM15|Nonvolatile (XMM), Volatile (upper half of YMM)|Must be preserved as needed by callee. YMM registers must be preserved as needed by caller.|  
+|XMM6:XMM15, YMM6:YMM15|Nonvolatile (XMM), Volatile (upper half of YMM)|Must be preserved by callee. YMM registers must be preserved as needed by caller.|  
 
 ## See Also  
  [x64 Software Conventions](../build/x64-software-conventions.md)   
- [__vectorcall](../cpp/vectorcall.md)
+ [__vectorcall](../cpp/vectorcall.md)