hwrng: bcm63xx - remove unused variables

These variables where left as unused in commit 6229c160
("hwrng: bcm63xx - make use of devm_hwrng_register")

Fixes the following warning:
drivers/char/hw_random/bcm63xx-rng.c: In function 'bcm63xx_rng_probe':
drivers/char/hw_random/bcm63xx-rng.c:85:16: warning: unused variable 'rng'
[-Wunused-variable]
  struct hwrng *rng;
                ^
drivers/char/hw_random/bcm63xx-rng.c:82:14: warning: unused variable 'clk'
[-Wunused-variable]
  struct clk *clk;

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>