iio: adc: meson-saradc: fix internal clock names

[ Upstream commit 50314f98b0ac468218e7c9af8c99f215a35436df ]

Before this patch we are registering the internal clocks (for example on
Meson8b, where the SAR ADC IP block implements the divider and gate
clocks) with the following names:
- /soc/cbus@c1100000/adc@8680#adc_div
- /soc/cbus@c1100000/adc@8680#adc_en

This is bad because the common clock framework uses the clock to create
a directory in <debugfs>/clk. With such name, the directory creation
(silently) fails and the debugfs entry ends up being created at the
debugfs root.

With this change, the new clock names are:
- c1108680.adc#adc_div
- c1108680.adc#adc_en

This matches the clock naming scheme used in the PWM, Ethernet and MMC
drivers. It also fixes the problem with debugfs.
The idea is shamelessly taken from commit b96e9eb6 ("pwm: meson:
Fix mux clock names").

Fixes: 3921db46 ("iio: Convert to using %pOF instead of full_name")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>