hw/i386/pc_piix.c: remove unnecessary if() from pc_init1()

hw/i386/pc_piix.c: remove unnecessary if() from pc_init1()

Now that the isapc logic has been split out of pc_piix.c, the PCI Host Bridge
(phb) object is now always set in pc_init1().

Since phb is now guaranteed not to be NULL, Coverity reports that the if()
statement surrounding ioapic_init_gsi() is now unnecessary and can be removed
along with the phb NULL initialiser.

Coverity: CID 1620557
Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Fixes: 99d0630a45 ("hw/i386/pc_piix.c: assume pcmc->pci_enabled is always true in pc_init1()")
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250901203409.1196620-1-mark.caveayland@nutanix.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>