at91rm9200: fix errors with CONFIG_CMD_I2C_TREE

This patch prevents linker error on AT91RM9200 boards, if
CONFIG_CMD_I2_TREE is set.
It implements i2c_set_bus_speed and i2c_get_bus_speed as a dummy function.

Signed-off-by: Jens Scharsig <esw@bus-elektronik.de>

cpu/arm920t/at91rm9200/i2c.c

@@ -203,4 +203,14 @@ void i2c_reg_write(uchar i2c_addr, uchar reg, uchar val)
 	i2c_write(i2c_addr, reg, 1, &val, 1);
 }
 
+int i2c_set_bus_speed(unsigned int speed)
+{
+	return -1;
+}
+
+unsigned int i2c_get_bus_speed(void)
+{
+	return CFG_I2C_SPEED;
+}
+
 #endif /* CONFIG_HARD_I2C */