When interrupt auto clear is programmed, any read to the interrupt
status register will clear all interrupts.  If two interrupts have
come in before one can be serviced then this will cause lost interrupts.

On AMD USB4 routers this has manifested in odd problems particularly
with long strings of control tranfers such as reading the DROM via bit
banging.

Instead of clearing interrupts automatically, clear the bit corresponding
to the given ring's interrupt in the ISR.

Fixes: 7a1808f8 ("thunderbolt: Handle ring interrupt by reading interrupt status register")
Cc: Sanju Mehta <Sanju.Mehta@amd.com>
Cc: stable@vger.kernel.org
Tested-by: Anson Tsao <anson.tsao@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>