PM: tools: Fix sleepgraph syntax error

The sleepgraph tool currently fails:

  File "/usr/bin/sleepgraph", line 4155
    or re.match('psci: CPU(?P<cpu>[0-9]*) killed.*', msg)):
                                                         ^
SyntaxError: unmatched ')'

Fixes: 34ea427e

 ("PM: tools: sleepgraph: Recognize "CPU killed" messages")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>