net: phy: realtek: Change rtlgen_get_speed() to rtlgen_decode_speed()

The value of the register to determine the speed, is retrieved
differently when using Clause 45 only. To use the rtlgen_get_speed()
function in this case, pass the value of the register as argument to
rtlgen_get_speed(). The function would then always return 0, so change it
to void. A better name for this function now is rtlgen_decode_speed().

Replace a call to genphy_read_status() followed by rtlgen_get_speed()
with a call to rtlgen_read_status() in rtl822x_read_status().

Add reading speed to rtl822x_c45_read_status().

Signed-off-by: Eric Woudstra <ericwouds@gmail.com>

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