nfp: Convert to use ERR_CAST()

Use ERR_CAST() as it is designed for casting an error pointer to
another type.
Signed-off-by: Shen Lichuan <shenlichuan@vivo.com>
Link: https://patch.msgid.link/20240829072538.33195-1-shenlichuan@vivo.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/netronome/nfp/nfpcore/nfp_nsp.c

@@ -278,7 +278,7 @@ struct nfp_nsp *nfp_nsp_open(struct nfp_cpp *cpp)
 
 	res = nfp_resource_acquire(cpp, NFP_RESOURCE_NSP);
 	if (IS_ERR(res))
-		return (void *)res;
+		return ERR_CAST(res);
 
 	state = kzalloc(sizeof(*state), GFP_KERNEL);
 	if (!state) {