Input: st-keyscan - disable interrupt while clock is gated

The driver gates off its peripheral clock when the input device is not
open and during system suspend without wakeup. However, the interrupt is
requested without IRQF_NO_AUTOEN and remains unmasked when the device is
stopped. If a pending or spurious interrupt fires while the clock is
disabled, keyscan_isr() will attempt to read the matrix state register
with the clock gated off, triggering a bus fault (synchronous external
abort) and panicking the system.

Request the interrupt with IRQF_NO_AUTOEN, enable it in keyscan_start(),
and disable it in keyscan_stop() prior to gating the clock. Drop the
pointless clock enable/stop sequence in keyscan_probe(), leaving the
clock gated and hardware untouched until the device is opened.

Fixes: 062589b13991 ("Input: add st-keyscan driver")
Reported-by: sashiko-bot@kernel.org
Assisted-by: LLM
Link: https://patch.msgid.link/apK-PZ5c97mCxBSC@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>