net: emaclite: fix compile warning in BUFFER_ALIGN

Use ulong instead of u32 to fix compile warning when building
kernel for arm64 (zynqmp):

drivers/net/ethernet/xilinx/xilinx_emaclite.c:98:42: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   98 | #define BUFFER_ALIGN(adr) ((ALIGNMENT - ((u32)adr)) % ALIGNMENT)
      |                                          ^

Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>