Fix typo in an error message

Author: gretay-js

backend/arm64/emit.mlp

@@ -165,7 +165,7 @@ let record_frame_label live dbg =
           Misc.fatal_error ("bad GC root " ^ Reg.name r)
       | { typ = Valx2; } as r ->
           (* CR mslater: (SIMD) arm64 *)
-          Misc.fatal_error ("Unexpect Valx2 type of reg " ^ Reg.name r)
+          Misc.fatal_error ("Unexpected Valx2 type of reg " ^ Reg.name r)
       | { typ = Val; loc = Unknown ; } as r ->
           Misc.fatal_error ("Unknown location " ^ Reg.name r)
       | { typ = Int | Float | Float32 | Vec128; _ } -> ())