rust: pci: get rid of redundant Result in IRQ methods

rust: pci: get rid of redundant Result in IRQ methods

Currently request_irq() returns

	Result<impl PinInit<irq::Registration<T>, Error> + 'a>

which may carry an error in the Result or the initializer; the same is
true for request_threaded_irq().

Use pin_init::pin_init_scope() to get rid of this redundancy.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251103203053.2348783-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>