x86: mm: fix VM_FAULT_RETRY handling

My commit 26178ec1 ("x86: mm: consolidate VM_FAULT_RETRY handling")
had a really stupid typo: the FAULT_FLAG_USER bit is in the 'flags'
variable, not the 'fault' variable. Duh,

The one silver lining in this is that Dave finding this at least
confirms that trinity actually triggers this special path easily, in a
way normal use does not.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>