x86/speculation: Fix typo IBRS_ATT, which should be IBRS_ALL

Fixes: 117cc7a9 ("x86/retpoline: Fill return stack buffer on vmexit")
Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20180202191220.blvgkgutojecxr3b@starbug-vm.ie.oracle.com

arch/x86/include/asm/nospec-branch.h

@@ -150,7 +150,7 @@ extern char __indirect_thunk_end[];
  * On VMEXIT we must ensure that no RSB predictions learned in the guest
  * can be followed in the host, by overwriting the RSB completely. Both
  * retpoline and IBRS mitigations for Spectre v2 need this; only on future
- * CPUs with IBRS_ATT *might* it be avoided.
+ * CPUs with IBRS_ALL *might* it be avoided.
  */
 static inline void vmexit_fill_RSB(void)
 {