ASoC: soc-core: fix debugfs_pop_time file permissions

I think this is a typo, debugfs_pop_time should not be executable.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Liam Girdwood <lrg@slimloogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>