sched/walt: fix lockdep warning from walt_update_min_max_capacity()

Below warning is observed while booting when lockdep is enabled.
Fix it by switching to spinlock nested call.

[    0.066452] WARNING: possible recursive locking detected
[    0.066681] Call trace:
[    0.066692]  dump_backtrace+0x0/0x190
[    0.066700]  show_stack+0x20/0x30
[    0.066712]  dump_stack+0xe8/0x13c
[    0.066721]  __lock_acquire+0x1c98/0x1e40
[    0.066727]  lock_acquire+0x1e0/0x218
[    0.066737]  _raw_spin_lock+0x40/0x58
[    0.066744]  walt_update_min_max_capacity+0x74/0x200
[    0.066754]  sched_cpu_activate+0x174/0x198
[    0.066764]  cpuhp_invoke_callback+0x540/0xd98
[    0.066771]  cpuhp_thread_fun+0x158/0x1b0
[    0.066781]  smpboot_thread_fn+0x1c8/0x2e8
[    0.066790]  kthread+0x11c/0x130
[    0.066798]  ret_from_fork+0x10/0x1c.

Change-Id: Ibc77ac55cc5fe4e8ab67a18ba0140067f80177b6
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>