hwrng: omap - Do not access INTMASK_REG on EIP76

hwrng: omap - Do not access INTMASK_REG on EIP76

The INTMASK_REG register does not exist on EIP76. Due to this, the call:

   omap_rng_write(priv, RNG_INTMASK_REG, RNG_SHUTDOWN_OFLO_MASK);

ends up, through the reg_map_eip76[] array, in accessing the register at
offset 0, which is the RNG_OUTPUT_0_REG. This by itself doesn't cause
any problem, but clearly doesn't enable the interrupt as it was
expected.

On EIP76, the register that allows to enable the interrupt is
RNG_CONTROL_REG. And just like RNG_INTMASK_REG, it's bit 1 of this
register that allows to enable the shutdown_oflo interrupt.

Fixes: 383212425c926 ("hwrng: omap - Add device variant for SafeXcel IP-76 found in Armada 8K")
Cc: <stable@vger.kernel.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>