ppc: Fix typo in TI_LOCAL_FLAGS definition

A typo crept in with commit ea1e847cc202e805769c3c46ba5e5c53714068a1
which defined TI_LOCAL_FLAGS to be the offset of the `flags' field
of struct thread_info, rather than the `local_flags' field.  This
fixes it.  The typo was pointed out by Guennadi Liakhovetski.

Signed-off-by: Paul Mackerras <paulus@samba.org>