avr32: Use correct condition around macb clock accessors

get_macb_pclk_rate() and get_macb_hclk_rate() should be available when
the chip has a MACB controller, not when it has a USART.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>

include/asm-avr32/arch-at32ap700x/clk.h

@@ -58,7 +58,7 @@ static inline unsigned long get_usart_clk_rate(unsigned int dev_id)
 	return get_pba_clk_rate();
 }
 #endif
-#ifdef AT32AP700x_CHIP_HAS_USART
+#ifdef AT32AP700x_CHIP_HAS_MACB
 static inline unsigned long get_macb_pclk_rate(unsigned int dev_id)
 {
 	return get_pbb_clk_rate();