net: mscc: ocelot: fix __ocelot_rmw_ix prototype

The "read-modify-write register index" function is declared with a
confusing prototype: the "mask" and "reg" arguments are swapped.

Fortunately, this does not affect callers so far. Both arguments are
u32, and the wrapper macros (ocelot_rmw_ix etc) have the arguments in
the correct order (the one from ocelot_io.c).

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>