perf: Merge consecutive conditionals in perf_mmap()

perf: Merge consecutive conditionals in perf_mmap()

  if (cond) {
    A;
  } else {
    B;
  }

  if (cond) {
    C;
  } else {
    D;
  }

into:

  if (cond) {
    A;
    C;
  } else {
    B;
    D;
  }

Notably the conditions are not identical in form, but are equivalent.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/20250812104018.900078502@infradead.org