PCI: keystone: Use devm_request_irq() to free "ks-pcie-error-irq" on exit

Commit under Fixes introduced the IRQ handler for "ks-pcie-error-irq".
The interrupt is acquired using "request_irq()" but is never freed if
the driver exits due to an error. Although the section in the driver that
invokes "request_irq()" has moved around over time, the issue hasn't been
addressed until now.

Fix this by using "devm_request_irq()" which automatically frees the
interrupt if the driver exits.

Fixes: 025dd3da ("PCI: keystone: Add error IRQ handler")
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Closes: https://lore.kernel.org/r/3d3a4b52-e343-42f3-9d69-94c259812143@kernel.org


Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20250912100802.3136121-2-s-vadapalli@ti.com