aarch64 - Set the mode for the unspec in speculation_tracker insn.

The speculation tracker insn in my recent patch set for CVE-2017-5753
was missing a mode on the UNSPEC.  Although this didn't break the
build, it did cause an unnecessary warning from the MD parsing
mechanism that I missed at the time.  It's a trivial fix, as follows:

	* config/aarch64/aarch64.md (speculation_tracker): Set the mode for
	the UNSPEC.

From-SVN: r265849

gcc/ChangeLog

+2018-11-06  Richard Earnshaw  <rearnsha@arm.com>
+
+	* config/aarch64/aarch64.md (speculation_tracker): Set the mode for
+	the UNSPEC.
+
 2018-11-06  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/86850
 	* vec.h (vec<T, va_heap, vl_ptr>::splice): Check src.length ()
 	instead of src.m_vec.
- 
+
 2018-11-06  Jan Hubicka  <jh@suse.cz>
 
 	* tree.c (fld_simplified_type_name): Break out form ...

gcc/config/aarch64/aarch64.md

@@ -6687,7 +6687,7 @@
 ;; SPECULATION_TRACKER_REGNUM is reserved for this purpose when necessary.
 (define_insn "speculation_tracker"
   [(set (reg:DI SPECULATION_TRACKER_REGNUM)
-	(unspec [(reg:DI SPECULATION_TRACKER_REGNUM) (match_operand 0)]
+	(unspec:DI [(reg:DI SPECULATION_TRACKER_REGNUM) (match_operand 0)]
 	 UNSPEC_SPECULATION_TRACKER))]
   ""
   {