This driver may take a regular spinlock when a raw spinlock
(irq_desc->lock) is already taken which results in the following
lockdep splat:

=============================
[ BUG: Invalid wait context ]
5.7.0-rc7 #1 Not tainted
-----------------------------
swapper/0/0 is trying to lock:
ffffff800303b798 (&chip_data->lock){....}-{3:3}, at: mtk_sysirq_set_type+0x48/0xc0
other info that might help us debug this:
context-{5:5}
2 locks held by swapper/0/0:
 #0: ffffff800302ee68 (&desc->request_mutex){....}-{4:4}, at: __setup_irq+0xc4/0x8a0
 #1: ffffff800302ecf0 (&irq_desc_lock_class){....}-{2:2}, at: __setup_irq+0xe4/0x8a0
stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.7.0-rc7 #1
Hardware name: Pumpkin MT8516 (DT)
Call trace:
 dump_backtrace+0x0/0x180
 show_stack+0x14/0x20
 dump_stack+0xd0/0x118
 __lock_acquire+0x8c8/0x2270
 lock_acquire+0xf8/0x470
 _raw_spin_lock_irqsave+0x50/0x78
 mtk_sysirq_set_type+0x48/0xc0
 __irq_set_trigger+0x58/0x170
 __setup_irq+0x420/0x8a0
 request_threaded_irq+0xd8/0x190
 timer_of_init+0x1e8/0x2c4
 mtk_gpt_init+0x5c/0x1dc
 timer_probe+0x74/0xf4
 time_init+0x14/0x44
 start_kernel+0x394/0x4f0

Replace the spinlock_t with raw_spinlock_t to avoid this warning.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200615074445.3579-1-brgl@bgdev.pl