omap: Overo: remove duplicate call to overo_ads7846_init()

overo_ads7846_init() is already called from overo_spi_init(), and
calling it twice is not only unnecessary but causes a warning as
"reg-fixed-voltage.1" is already added to the device tree.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>