avr32: Fix .size directive for cpu_enter_idle

gas used to accept (and ignore?) .size directives which referred to
undefined symbols, as this does.  In binutils 2.21 these are treated
as errors.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

arch/avr32/mach-at32ap/pm-at32ap700x.S

@@ -53,7 +53,7 @@ cpu_enter_idle:
 	st.w	r8[TI_flags], r9
 	unmask_interrupts
 	sleep	CPU_SLEEP_IDLE
-	.size	cpu_idle_sleep, . - cpu_idle_sleep
+	.size	cpu_enter_idle, . - cpu_enter_idle
 
 	/*
 	 * Common return path for PM functions that don't run from