spi: hisi-kunpeng: Fix Woverflow warning on conversion

Fix warning Woverflow on type conversion reported on x86_64:

  drivers/spi/spi-hisi-kunpeng.c:361:9: warning: conversion from 'long unsigned int' to 'u32'
  {aka 'unsigned int'} changes value from '18446744073709551600' to '4294967280' [-Woverflow]

The registers are 32 bit, so fix by casting to u32.

Fixes: c770d863 ("spi: Add HiSilicon SPI Controller Driver for Kunpeng SoCs")
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jay Fang <f.fangjian@huawei.com>
Link: https://lore.kernel.org/r/1617762660-54681-1-git-send-email-f.fangjian@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>