net/mlx5e: Remove the outer loop when allocating legacy RQ WQEs

Legacy RQ WQEs are allocated in a loop in small batches (8 WQEs). As
partial batches are allowed, there is no point to have a loop in a loop,
so the outer loop is removed, and the batch size is increased up to the
total number of WQEs to allocate, still not smaller than 8.

Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>