irqchip/loongarch-cpu: Fix return value of lpic_gsi_to_irq()

lpic_gsi_to_irq() should return a valid Linux interrupt number if
acpi_register_gsi() succeeds, and return 0 otherwise. But lpic_gsi_to_irq()
converts a negative return value of acpi_register_gsi() to a positive value
silently.

Convert the return value explicitly.

Fixes: e8bba72b ("irqchip / ACPI: Introduce ACPI_IRQ_MODEL_LPIC for LoongArch")
Reported-by: Miao Wang <shankerwangmiao@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20240723064508.35560-1-chenhuacai@loongson.cn

drivers/irqchip/irq-loongarch-cpu.c

@@ -18,11 +18,13 @@ struct fwnode_handle *cpuintc_handle;
 
 static u32 lpic_gsi_to_irq(u32 gsi)
 {
+	int irq = 0;
+
 	/* Only pch irqdomain transferring is required for LoongArch. */
 	if (gsi >= GSI_MIN_PCH_IRQ && gsi <= GSI_MAX_PCH_IRQ)
-		return acpi_register_gsi(NULL, gsi, ACPI_LEVEL_SENSITIVE, ACPI_ACTIVE_HIGH);
+		irq = acpi_register_gsi(NULL, gsi, ACPI_LEVEL_SENSITIVE, ACPI_ACTIVE_HIGH);
 
-	return 0;
+	return (irq > 0) ? irq : 0;
 }
 
 static struct fwnode_handle *lpic_get_gsi_domain_id(u32 gsi)