net: gem: Reduce timeout of mdio phy idle status check

Timeout for checking mdio phy idle status is 20seconds. In case of errors
this timeout will be too much. Reduce it to 100ms.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Link: https://lore.kernel.org/r/1b73aa57b77587391e1bcd6d9f0480163367ed1b.1637237121.git.michal.simek@xilinx.com