net: dsa: bcm_sf2: Use correct I/O accessors

The Starfigther 2 driver currently uses __raw_{read,write}l which means
native I/O endian. This works correctly for an ARM LE kernel (default)
but fails miserably on an ARM BE (BE8) kernel where registers are kept
little endian, so replace uses with {read,write}l_relaxed here which is
what we want because this is all performance sensitive code.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>