bnxt_en: eliminate the compile warning in bnxt_request_irq due to CONFIG_RFS_ACCEL

I received a kernel-test-bot report[1] that shows the
[-Wunused-but-set-variable] warning. Since the previous commit I made, as
the 'Fixes' tag shows, gives users an option to turn on and off the
CONFIG_RFS_ACCEL, the issue then can be discovered and reproduced with
GCC specifically.

Like Simon and Jakub suggested, use fewer #ifdefs which leads to fewer
bugs.

[1]
All warnings (new ones prefixed by >>):

   drivers/net/ethernet/broadcom/bnxt/bnxt.c: In function 'bnxt_request_irq':
>> drivers/net/ethernet/broadcom/bnxt/bnxt.c:10703:9: warning: variable 'j' set but not used [-Wunused-but-set-variable]
   10703 |  int i, j, rc = 0;
         |         ^

Fixes: 9b6a30fe ("net: allow rps/rfs related configs to be switched")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506282102.x1tXt0qz-lkp@intel.com/


Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>