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

BugLink: https://bugs.launchpad.net/bugs/1797563

commit 8f318526 upstream.

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>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.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;
 }