spi: spi-mem: Fix code indent should use tabs where possible

Fix checkpatch errors:

  ERROR: code indent should use tabs where possible
  #624: FILE: spi-mem.c:624:
  ERROR: code indent should use tabs where possible
  #626: FILE: spi-mem.c:626:
  ERROR: code indent should use tabs where possible
  #627: FILE: spi-mem.c:627:
Signed-off-by: Jay Fang <f.fangjian@huawei.com>
Link: https://lore.kernel.org/r/1616566602-13894-10-git-send-email-f.fangjian@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>