i386: fix a hang on stuck nmi watchdog

In the case when an nmi gets stucks the endflag stays equal to zero.
This causes the busy looping on other cpus to continue, even though the
nmi test is done.

On my machine with out the change below the system would hang right
after check_nmi_watchdog().  The change below just sets endflag prior to
checking if the test was successful or not.

Signed-off-by: Daniel Walker <dwalker@mvista.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>