irqchip/loongson-pci-msi: Fix a typo in Kconfig

PCH MSI driver's menuconfig entry was wrong. Fix it.

Fixes: 632dcc2c ("irqchip: Add Loongson PCH MSI controller")
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200530121113.1797678-2-jiaxun.yang@flygoat.com