cpumask: Fix typo nr_cpumask_size --> nr_cpumask_bits

The never used nr_cpumask_size is just a typo, hence use existing
redefinition that's called nr_cpumask_bits.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/cpumask.h

@@ -66,7 +66,7 @@ static inline void set_nr_cpu_ids(unsigned int nr)
  *
  * Finally, some operations just want the exact limit, either because
  * they set bits or just don't have any faster fixed-sized versions. We
- * call this just 'nr_cpumask_size'.
+ * call this just 'nr_cpumask_bits'.
  *
  * Note that these optional constants are always guaranteed to be at
  * least as big as 'nr_cpu_ids' itself is, and all our cpumask