net: ravb: Use tabs instead of spaces

Use tabs instead of spaces in the ravb_set_rate_gbeth() function.
This aligns with the coding style requirements.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>