regmap: Ensure regmap_register_patch() is compatible with fast_io

With fast_io we use mutexes to lock the I/O operations so we would need
to do GFP_ATOMIC allocations if we wanted to do allocations inside the
lock as we do currently. Since it is unlikely that we will want to register
a patch outside of init where concurrency shouldn't be an issue move the
allocation of the patch data outside the lock.

Reported-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@linaro.org>