x86/srat: Simplify memory affinity init error handling

The acpi_numa_memory_affinity_init() function can fail in
several scenarios, use a single point of error return.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Link: http://lkml.kernel.org/r/1357690721.1890.15.camel@buesod1.americas.hpqcorp.net
[ Cleaned up the label naming a bit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>