MIPS: AR7: remove orphan declarations from arch/mips/include/asm/mach-ar7/ar7.h

All uses of ar7_cpu_clock, ar7_bus_clock and ar7_dsp_clock were
removed by commit 780019dd ("MIPS: AR7: Implement clock API"),
so remove the orphan declarations, too.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/mach-ar7/ar7.h

@@ -104,8 +104,6 @@ struct plat_dsl_data {
 	int reset_bit_sar;
 };
 
-extern int ar7_cpu_clock, ar7_bus_clock, ar7_dsp_clock;
-
 static inline int ar7_is_titan(void)
 {
 	return (readl((void *)KSEG1ADDR(AR7_REGS_GPIO + 0x24)) & 0xffff) ==