net: phy: ti: Fix clock output DT property

The code block reading the DT property for the clock output control was
before the phy's DT node pointer was set, so it could never work.  Move
it after the node pointer is set.

Also store the unsigned 32-bit property into an unsigned value, not a
signed value, as the former will cause a problem if value overflows.
For instance, if one were to add 0xffffffff as a code to mean the clock
output should be turned off.

Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Janine Hagemann <j.hagemann@phytec.de>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>