Tegra210: Fix 64-bit build warning about save_boot_params_ret()

Simon's 'tegra124: Implement spl_was_boot_source()' needs
a prototype for save_boot_params_ret() to build cleanly
for 64-bit Tegra210.

Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/mach-tegra/board.c

@@ -18,6 +18,8 @@
 #include <asm/arch-tegra/sys_proto.h>
 #include <asm/arch-tegra/warmboot.h>
 
+void save_boot_params_ret(void);
+
 DECLARE_GLOBAL_DATA_PTR;
 
 enum {