x86/kconfig: Fix the CONFIG_NR_CPUS description

x86/kconfig: Fix the CONFIG_NR_CPUS description

Since:

  b53b5eda8194 ("x86/cpu: Increase max CPU count to 8192")

... the maximum supported NR_CPUS for CPUMASK_OFFSTACK case
is 8192. Let's adjust the description to reflect the change.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1431080726-2490-1-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>