Currently, the code that takes a reference to the clock and enables it
is located inside of_get_omap_rng_device_details(), called only when
probing through the Device Tree.

However, there is nothing that makes this clock logic dependent on the
Device Tree, so it makes more sense to have it in omap_rng_probe()
directly.

Moreover, we make sure to bail out if we can't enable the clock. Indeed,
while the clock is optional, if a clock is present, we really want to
succeed in enabling it. And we fix the error message to fit on one line,
so that it is grep-friendly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>