Input: imx6ul_tsc - convert int to u32

The code uses of_property_read_u32 and expects positive values.  However,
the values are stored in signed int variables.  Additionally, the registers
values are also stored in signed variables without a good reason
(readl/writel expect u32).

The only time this caused a real bug was in the new average-samples
property, in which the property is numerically compared and implicitly
expected to be positive.

I believe it's better to change all the properties and registers to u32,
for consistency and warnings reduction.

Signed-off-by: Guy Shapiro <guy.shapiro@mobi-wize.com>
Reported-by: Bjørn Forsman <bjorn.forsman@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>