common: return type board_get_usable_ram_top

board_get_usable_ram_top() returns a physical address that is stored in
gd->ram_top. The return type of the function should be phys_addr_t like the
current type of gd->ram_top.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/board/imgtec/boston/ddr.c b/board/imgtec/boston/ddr.c
index 8532225..cecf454 100644
--- a/board/imgtec/boston/ddr.c
+++ b/board/imgtec/boston/ddr.c
@@ -23,7 +23,7 @@
 	return 0;
 }
 
-phys_size_t board_get_usable_ram_top(phys_size_t total_size)
+phys_addr_t board_get_usable_ram_top(phys_size_t total_size)
 {
 	DECLARE_GLOBAL_DATA_PTR;