net: mdio device: use flexible sleeping in reset function

MDIO device reset assert and deassert length was created by
usleep_range() but that does not ensure optimal handling of
all the different values from device tree properties.
By switching to the new flexible sleeping helper function,
fsleep(), the correct delay function is called depending on
delay length, e.g. udelay(), usleep_range() or msleep().

Signed-off-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>