Fixes the following checkpatch errors:

ERROR: do not use assignment in if condition

Signed-off-by: Ran Sun <sunran001@208suo.com>
---
  arch/x86/kernel/apic/io_apic.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/apic/io_apic.c 
b/arch/x86/kernel/apic/io_apic.c
index 4241dc243aa8..be32b085d37e 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1058,8 +1058,11 @@ static int mp_map_pin_to_irq(u32 gsi, int idx, 
int ioapic, int pin,
  		if (legacy)
  			irq = alloc_isa_irq_from_domain(domain, irq,
  							ioapic, pin, &tmp);
-		else if ((irq = irq_find_mapping(domain, pin)) == 0)
-			irq = alloc_irq_from_domain(domain, ioapic, gsi, &tmp);
+		else {
+			irq = irq_find_mapping(domain, pin);
+			if (irq == 0)
+				irq = alloc_irq_from_domain(domain, ioapic, gsi, &tmp);
+		}
  		else if (!mp_check_pin_attr(irq, &tmp))
  			irq = -EBUSY;
  		if (irq >= 0) {