net: dsa: microchip: Replace ksz9477_wait_alu_sta_ready polling with regmap

Regmap provides polling function to poll for bits in a register. This
function is another reimplementation of polling for bit being clear in
a register. Replace this with regmap polling function. Moreover, inline
the function parameters, as the function is never called with any other
parameter values than this one.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Cc: Woojung Huh <Woojung.Huh@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>