PCI: xilinx-nwl: Fix off-by-one in INTx IRQ handler

PCI: xilinx-nwl: Fix off-by-one in INTx IRQ handler

commit 0199d2f2bd8cd97b310f7ed82a067247d7456029 upstream.

MSGF_LEG_MASK is laid out with INTA in bit 0, INTB in bit 1, INTC in bit 2,
and INTD in bit 3. Hardware IRQ numbers start at 0, and we register
PCI_NUM_INTX IRQs. So to enable INTA (aka hwirq 0) we should set bit 0.
Remove the subtraction of one.

This bug would cause INTx interrupts not to be delivered, as enabling INTB
would actually enable INTA, and enabling INTA wouldn't enable anything at
all. It is likely that this got overlooked for so long since most PCIe
hardware uses MSIs. This fixes the following UBSAN error:

  UBSAN: shift-out-of-bounds in ../drivers/pci/controller/pcie-xilinx-nwl.c:389:11
  shift exponent 18446744073709551615 is too large for 32-bit type 'int'
  CPU: 1 PID: 61 Comm: kworker/u10:1 Not tainted 6.6.20+ #268
  Hardware name: xlnx,zynqmp (DT)
  Workqueue: events_unbound deferred_probe_work_func
  Call trace:
  dump_backtrace (arch/arm64/kernel/stacktrace.c:235)
  show_stack (arch/arm64/kernel/stacktrace.c:242)
  dump_stack_lvl (lib/dump_stack.c:107)
  dump_stack (lib/dump_stack.c:114)
  __ubsan_handle_shift_out_of_bounds (lib/ubsan.c:218 lib/ubsan.c:387)
  nwl_unmask_leg_irq (drivers/pci/controller/pcie-xilinx-nwl.c:389 (discriminator 1))
  irq_enable (kernel/irq/internals.h:234 kernel/irq/chip.c:170 kernel/irq/chip.c:439 kernel/irq/chip.c:432 kernel/irq/chip.c:345)
  __irq_startup (kernel/irq/internals.h:239 kernel/irq/chip.c:180 kernel/irq/chip.c:250)
  irq_startup (kernel/irq/chip.c:270)
  __setup_irq (kernel/irq/manage.c:1800)
  request_threaded_irq (kernel/irq/manage.c:2206)
  pcie_pme_probe (include/linux/interrupt.h:168 drivers/pci/pcie/pme.c:348)

Fixes: 9a181e1093af ("PCI: xilinx-nwl: Modify IRQ chip for legacy interrupts")
Link: https://lore.kernel.org/r/20240531161337.864994-3-sean.anderson@linux.dev
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>