riscv: ax25-ae350: Cast addr with uintptr_t

addr was delcared as fdt_addr_t which is now a 64-bit address.
In a 32-bit build, this causes the following warning seen when
building ax25-ae350.c:

  warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

Cast addr with uintptr_t.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
diff --git a/board/AndesTech/ax25-ae350/ax25-ae350.c b/board/AndesTech/ax25-ae350/ax25-ae350.c
index 59a43e4..3125233 100644
--- a/board/AndesTech/ax25-ae350/ax25-ae350.c
+++ b/board/AndesTech/ax25-ae350/ax25-ae350.c
@@ -77,7 +77,7 @@
 	if (addr == FDT_ADDR_T_NONE)
 		return -EINVAL;
 
-	regs = (struct ftsmc020_bank *)addr;
+	regs = (struct ftsmc020_bank *)(uintptr_t)addr;
 	regs->cr &= ~FTSMC020_BANK_WPROT;
 
 	return 0;