regmap: debugfs: Don't sleep while atomic for fast_io regmaps

If a regmap has "fast_io" set then its lock function uses a spinlock.
That doesn't work so well with the functions:
* regmap_cache_only_write_file()
* regmap_cache_bypass_write_file()

Both of the above functions have the pattern:
1. Lock the regmap.
2. Call:
   debugfs_write_file_bool()
     copy_from_user()
       __might_fault()
         __might_sleep()

Let's reorder things a bit so that we do all of our sleepable
functions before we grab the lock.

Fixes: d3dc5430

 ("regmap: debugfs: Allow writes to cache state settings")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200715164611.1.I35b3533e8a80efde0cec1cc70f71e1e74b2fa0da@changeid


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