irqchip/gic-v3: Add missing barrier to 32bit version of gic_read_iar()

Commit 1a1ebd5f ("irqchip/gic-v3: Make sure read from ICC_IAR1_EL1 is
visible on redestributor") fixed the missing barrier on arm64, but
forgot to update the 32bit counterpart, which has the same requirements.
Let's fix it.

Fixes: 1a1ebd5f ("irqchip/gic-v3: Make sure read from ICC_IAR1_EL1 is visible on redestributor")
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/include/asm/arch_gicv3.h

@@ -117,6 +117,7 @@ static inline u32 gic_read_iar(void)
 	u32 irqstat;
 
 	asm volatile("mrc " __stringify(ICC_IAR1) : "=r" (irqstat));
+	dsb(sy);
 	return irqstat;
 }