ASoC: SOF: Disable pointless writes to debugfs file

The permissions on this debugfs file are 0444 so it can't be written to.
And writing to the file hasn't done anything since commit 6e9548cd
("ASoC: SOF: Convert the generic IPC flood test into SOF client").
Delete the write function.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://msgid.link/r/9d2477cf-25aa-4d12-818f-fdafc9aaa28a@moroto.mountain


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