serial: altera_uart: convert to livetree

Convert 'altera_uart_ofdata_to_platdata' to use 'dev_read_u32_default'
instead of 'fdtdec_get_int' and get rid of DECLARE_GLOBAL_DATA_PTR.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
diff --git a/drivers/serial/altera_uart.c b/drivers/serial/altera_uart.c
index 67d4719..436cf23 100644
--- a/drivers/serial/altera_uart.c
+++ b/drivers/serial/altera_uart.c
@@ -10,8 +10,6 @@
 #include <serial.h>
 #include <asm/io.h>
 
-DECLARE_GLOBAL_DATA_PTR;
-
 /* status register */
 #define ALTERA_UART_TMT		BIT(5)	/* tx empty */
 #define ALTERA_UART_TRDY	BIT(6)	/* tx ready */
@@ -91,8 +89,7 @@
 	plat->regs = map_physmem(devfdt_get_addr(dev),
 				 sizeof(struct altera_uart_regs),
 				 MAP_NOCACHE);
-	plat->uartclk = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev),
-		"clock-frequency", 0);
+	plat->uartclk = dev_read_u32_default(dev, "clock-frequency", 0);
 
 	return 0;
 }