powerpc/8xxx: Replace fsl_ddr_get_mem_data_rate with get_ddr_freq()

Every 85xx board implements fsl_ddr_get_mem_data_rate via get_ddr_freq()
and every 86xx board uses get_bus_freq().  If implement get_ddr_freq()
as a static inline to call get_bus_freq() we can remove
fsl_ddr_get_mem_data_rate altogether and just call get_ddr_freq()
directly.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/board/freescale/mpc8641hpcn/ddr.c b/board/freescale/mpc8641hpcn/ddr.c
index 8dc249b..07bb92f 100644
--- a/board/freescale/mpc8641hpcn/ddr.c
+++ b/board/freescale/mpc8641hpcn/ddr.c
@@ -18,11 +18,6 @@
 	i2c_read(i2c_address, 0, 1, (uchar *)spd, sizeof(ddr2_spd_eeprom_t));
 }
 
-unsigned int fsl_ddr_get_mem_data_rate(void)
-{
-	return get_bus_freq(0);
-}
-
 void fsl_ddr_get_spd(ddr2_spd_eeprom_t *ctrl_dimms_spd,
 		      unsigned int ctrl_num)
 {
@@ -144,7 +139,7 @@
 	/* Get clk_adjust, cpo, write_data_delay, according to the board ddr
 	 * freqency and n_banks specified in board_specific_parameters table.
 	 */
-	ddr_freq = fsl_ddr_get_mem_data_rate() / 1000000;
+	ddr_freq = get_ddr_freq(0) / 1000000;
 	for (j = 0; j < CONFIG_DIMM_SLOTS_PER_CTLR; j++) {
 		if (pdimm[j].n_ranks > 0) {
 			for (i = 0; i < num_params; i++) {