irqdomain: Drop dead domain-name assignment

Since commit d59f6617 ("genirq: Allow fwnode to carry name
information only") an IRQ domain is always given a name during
allocation (e.g. used for the debugfs entry).

Drop the leftover name assignment when allocating the first IRQ.

Tested-by: Hsin-Yi Wang <hsinyi@chromium.org>
Tested-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230213104302.17307-10-johan+linaro@kernel.org