UPSTREAM: x86/speculation: Update link to AMD speculation whitepaper

commit e9b6013a7ce31535b04b02ba99babefe8a8599fa upstream.

Update the link to the "Software Techniques for Managing Speculation
on AMD Processors" whitepaper.

Bug: 215557547
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I65521b935a50147f7c694f00f292add8bf2385bc