net: phy: TI DP83869 fix invalid clock delay configuration

Setting the clock delay from the device tree settings
rx-internal-delay-ps and tx-internal-delay-ps was broken:

 - The expected value in the device tree is suppose to be a
   delay in picoseconds, but the driver only allowed an array index.
 - Driver converted this array index to the actual delay in
   picoseconds and tried to apply this in the device register. This
   however is not a valid register value. The actual logic here was
   reversed, it converted an register representation of the delay to
   the device tree delay in picoseconds.

Only when the internal delays were NOT configured in the device tree
and they default value of 7 (=2000ps) was used, a valid value was
loaded in the register.

Signed-off-by: Frank de Brabander <debrabander@gmail.com>