x86/topology: Fix function name in documentation

topology_sibling_cpumask() is the correct thread-related topology
function in the kernel:

s/topology_sibling_mask/topology_sibling_cpumask

Signed-off-by: Dou Liyang <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

Documentation/x86/topology.txt

···
 
     The number of online threads is also printed in /proc/cpuinfo "siblings."
 
-  - topology_sibling_mask():
+  - topology_sibling_cpumask():
 
     The cpumask contains all online threads in the core to which a thread
     belongs.