tools/testing/selftests: fix uninitialized variable

The err variable is intended to receive the timer_create() return before
checking it

Signed-off-by: Felipe Pena <felipensp@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>