crypto: cavium/nitrox - don't cast parameter in bit operations

While in this particular case it would not be a (critical) issue,
the pattern itself is bad and error prone in case the location
of the parameter is changed.

Don't cast parameter to unsigned long pointer in the bit operations.
Instead copy to a local variable on stack of a proper type and use.

Fixes: cf718eaa ("crypto: cavium/nitrox - Enabled Mailbox support")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>