hwrng: imx-rngc - irq already prints an error

Clean up the check for irq. dev_err() is superfluous as
platform_get_irq() already prints an error. Check for zero
would indicate a bug. Remove curly braces to conform to
styling requirements.
Signed-off-by: Nigel Christian <nigel.l.christian@gmail.com>

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>