net: stmmac: stm32: simplify clock handling

Some stm32 implementations need the receive clock running in suspend,
as indicated by dwmac->ops->clk_rx_enable_in_suspend. The existing
code achieved this in a rather complex way, by passing a flag around.

However, the clk API prepare/enables are counted - which means that a
clock won't be stopped as long as there are more prepare and enables
than disables and unprepares, just like a reference count.

Therefore, we can simplify this logic by calling clk_prepare_enable()
an additional time in the probe function if this flag is set, and then
balancing that at remove time.

With this, we can avoid passing a "are we suspending" and "are we
resuming" flag to various functions in the driver.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>