irqchip/mips-gic: Use bitfield helpers

Use the FIELD_GET() helper, instead of open-coding the same operation.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/all/74f9d126961a90d3e311b92a54870eaac5b3ae57.1637593297.git.geert+renesas@glider.be

drivers/irqchip/irq-mips-gic.c

@@ -9,6 +9,7 @@
 
 #define pr_fmt(fmt) "irq-mips-gic: " fmt
 
+#include <linux/bitfield.h>
 #include <linux/bitmap.h>
 #include <linux/clocksource.h>
 #include <linux/cpuhotplug.h>
@@ -735,8 +736,7 @@ static int __init gic_of_init(struct device_node *node,
 	mips_gic_base = ioremap(gic_base, gic_len);
 
 	gicconfig = read_gic_config();
-	gic_shared_intrs = gicconfig & GIC_CONFIG_NUMINTERRUPTS;
-	gic_shared_intrs >>= __ffs(GIC_CONFIG_NUMINTERRUPTS);
+	gic_shared_intrs = FIELD_GET(GIC_CONFIG_NUMINTERRUPTS, gicconfig);
 	gic_shared_intrs = (gic_shared_intrs + 1) * 8;
 
 	if (cpu_has_veic) {