iio: Remove kernel-doc keyword in file header comment

Remove kernel-doc keyword from function header comment.
It fixes issues spotted by scripts/kernel-doc like:
drivers/iio/<driver>.c:3: info: Scanning doc for function <component name>
drivers/iio/<driver>.c:X: warning: expecting prototype for <component name>.
  Prototype was for <function>() instead

To reproduce the errors:
scripts/kernel-doc -v -none $(find drivers/iio/ -name \*.c \
-exec head -2 {} \+ | grep -B2 -e '\*\*' | grep '==' | cut -d ' ' -f 2)

After, confirm these errors are gone with:
scripts/kernel-doc -v -none $(git show --name-only  | grep -e "^driver")

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Link: https://lore.kernel.org/r/20210309234314.2208256-1-gwendal@chromium.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>