Fix vmv.v.v vd. vd typo (riscv#1899)

Author: pfusik

src/v-st-ext.adoc

@@ -3039,7 +3039,7 @@ can shuffle the internal representation according to SEW.
 Implementations that do not internally reorganize data can dynamically
 elide this instruction, and treat as a NOP.
 
-NOTE: The `vmv.v.v vd. vd` instruction is not a RISC-V HINT as a
+NOTE: The `vmv.v.v vd, vd` instruction is not a RISC-V HINT as a
 tail-agnostic setting may cause an architectural state change on some
 implementations.