ARM: davinci: WARN_ON() if clk_get() fails

Currently the timer code checks if the clock pointer passed to it is
good (!IS_ERR(clk)). The new clocksource driver expects the clock to
be functional and doesn't perform any checks so emit a warning if
clk_get() fails. Apply this to all davinci platforms.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>