mlxsw: spectrum_router: simplify list unwinding

mlxsw: spectrum_router: simplify list unwinding

The setting of i here
err_nexthop6_group_get:
	i = nrt6;
Is redundant, i is already nrt6.  So remove
this statement.

The for loop for the unwinding
err_rt6_create:
	for (i--; i >= 0; i--) {
Is equivelent to
	for (; i > 0; i--) {

Two consecutive labels can be reduced to one.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20220402121516.2750284-1-trix@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>