pid: cleanup the stale comment mentioning pidmap_init().

pidmap_init() has already been replaced with pid_idr_init() in the commit
95846ec ("pid: replace pid bitmap implementation with IDR API").
Cleanup the stale comment which still mentions it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Takahiro Itazuri <[email protected]>
Cc: Kuniyuki Iwashima <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: zulinx86

include/linux/threads.h

@@ -38,7 +38,7 @@
  * Define a minimum number of pids per cpu.  Heuristically based
  * on original pid max of 32k for 32 cpus.  Also, increase the
  * minimum settable value for pid_max on the running system based
- * on similar defaults.  See kernel/pid.c:pidmap_init() for details.
+ * on similar defaults.  See kernel/pid.c:pid_idr_init() for details.
  */
 #define PIDS_PER_CPU_DEFAULT	1024
 #define PIDS_PER_CPU_MIN	8