powerpc: Return the_cpu_ spec from identify_cpu

Commit af9eef3c7b1ed004c378c89b87642f4937337d50 caused cpu_setup to see
the_cpu_spec, rather than the source struct.  However, on 32-bit, the
return value of identify_cpu was being used for feature fixups, and
identify_cpu was returning the source struct.  So if cpu_setup patches
the feature bits, the update won't affect the fixups.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>