phy: marvell: Fix off by 1 limit checks

phy: marvell: Fix off by 1 limit checks

The limit checks in get_speed_string and get_type_string are off by 1 as
they do not account for the maximum index into an array that can be used
is 1 less than the number of elements in that array. Adjust the limit
checks to allow for this.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Stefan Roese <stefan.roese@mailbox.org>