powerpc/mpc85xx: explicit cast the SDRAM size to type phys_size_t

To avoid sign extension problem, use explicit casting to cast
the SDRAM size to type phys_size_t, or else, if the SDRAM size
is 2G(0x80000000), it will be extended to 0xffffffff80000000
when phys_size_t is type 'unsigned long long'.

Signed-off-by: Mingkai Hu <Mingkai.Hu@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>

arch/powerpc/cpu/mpc85xx/cpu.c

@@ -341,7 +341,7 @@ phys_size_t initdram(int board_type)
 #if defined(CONFIG_SPD_EEPROM) || defined(CONFIG_DDR_SPD)
 	return fsl_ddr_sdram_size();
 #else
-	return CONFIG_SYS_SDRAM_SIZE * 1024 * 1024;
+	return (phys_size_t)CONFIG_SYS_SDRAM_SIZE * 1024 * 1024;
 #endif
 }
 #else /* CONFIG_SYS_RAMBOOT */