ice: switch: Simplify memory allocation

'rbuf' is locale to the ice_get_initial_sw_cfg() function.
There is no point in using devm_kzalloc()/devm_kfree().

use kzalloc()/kfree() instead.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>