DT: mxs-lradc: fix ranges of ts properties

This patch fixes off-by-one issues in the devicetree binding of
mxs-lradc.

According to the i.MX23 and i.MX28 reference manuals [1][2] the range of
NUM_SAMPLES is 0..31, but property ave-ctrl is substracted by 1 before used.

Considering all limitations the range of DELAY is 1..2047, but also
property ave-delay is substracted by 1 before used.

The patch has been suggested by Hartmut Knaack and Kristina Martsenko.

[1] - http://cache.freescale.com/files/dsp/doc/ref_manual/IMX23RM.pdf
[2] - http://cache.freescale.com/files/dsp/doc/ref_manual/MCIMX28RM.pdf

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt

@@ -12,9 +12,9 @@ Optional properties:
                                property is not present, then the touchscreen is
                                disabled. 5 wires is valid for i.MX28 SoC only.
 - fsl,ave-ctrl: number of samples per direction to calculate an average value.
-                Allowed value is 1 ... 31, default is 4
+                Allowed value is 1 ... 32, default is 4
 - fsl,ave-delay: delay between consecutive samples. Allowed value is
-                 1 ... 2047. It is used if 'fsl,ave-ctrl' > 1, counts at
+                 2 ... 2048. It is used if 'fsl,ave-ctrl' > 1, counts at
                  2 kHz and its default is 2 (= 1 ms)
 - fsl,settling: delay between plate switch to next sample. Allowed value is
                 1 ... 2047. It counts at 2 kHz and its default is