staging: iio: fix warning 'static but used in inline function'

iio_utils.h:367:10: warning: ‘iioutils_break_up_name’ is static but used in inline function ‘build_channel_array’ which is not static [enabled by default]

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>