staging: iio: isl29018: remove the FSF's mailing address

Address warning from checkpatch:

CHECK: Do not include the paragraph about writing to the Free Software
Foundation's mailing address from the sample GPL notice. The FSF has
changed addresses in the past, and may do so again. Linux already
includes a copy of the GPL.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>