x86/spectre: Fix an error message

If i == ARRAY_SIZE(mitigation_options) then we accidentally print
garbage from one space beyond the end of the mitigation_options[] array.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: KarimAllah Ahmed <karahmed@amazon.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Fixes: 9005c683 ("x86/spectre: Simplify spectre_v2 command line parsing")
Link: http://lkml.kernel.org/r/20180214071416.GA26677@mwanda


Signed-off-by: Ingo Molnar <mingo@kernel.org>