phy: ocelot-serdes: fix out-of-bounds read

Currently, there is an out-of-bounds read on array ctrl->phys,
once variable i reaches the maximum array size of SERDES_MAX
in the for loop.

Fix this by changing the condition in the for loop from
i <= SERDES_MAX to i < SERDES_MAX.

Addresses-Coverity-ID: 1473966 ("Out-of-bounds read")
Addresses-Coverity-ID: 1473959 ("Out-of-bounds read")
Fixes: 51f6b410fc22 ("phy: add driver for Microsemi Ocelot SerDes muxing")
Reviewed-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
