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/arch/riscv/cpu/fu540/dram.c b/arch/riscv/cpu/fu540/dram.c
index 44e11bd..94d8018 100644
--- a/arch/riscv/cpu/fu540/dram.c
+++ b/arch/riscv/cpu/fu540/dram.c
@@ -21,7 +21,7 @@
 	return fdtdec_setup_memory_banksize();
 }
 
-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)
 {
 	/*
 	 * Ensure that we run from first 4GB so that all