cmd/compile: fix doc typo in ssa.go

Change-Id: Ie299a5eca6f6a7c5a37c00ff0de7ce322450375b
Reviewed-on: https://go-review.googlesource.com/c/go/+/178123Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/ssa.go

@@ -5123,7 +5123,7 @@ func (s *SSAGenState) Br(op obj.As, target *ssa.Block) *obj.Prog {
 	return p
 }
 
-// DebugFriendlySetPos adjusts Pos.IsStmt subject to heuristics
+// DebugFriendlySetPosFrom adjusts Pos.IsStmt subject to heuristics
 // that reduce "jumpy" line number churn when debugging.
 // Spill/fill/copy instructions from the register allocator,
 // phi functions, and instructions with a no-pos position