net: lpc32xx: fix ignored MDIO busy wait status on read

The change fixes PHY write operation, which incorrectly waits for
released busy state before issuing a write operation, this breaks
sequential write/read operation logic, because read operation
starts immediately on request and it completes, when busy state is
gone.

Instead of adding the second preceding busy state check to read
function, do busy state release check after issuing a write operation,
this method of operation is also recommended by the LPC32xx User's
Manual, see MII Mgmt Indicators Register notes:

  For PHY Write if scan is not used:
  1. Write 0 to MCMD
  2. Write PHY address and register address to MADR
  3. Write data to MWTD
  4. Wait for busy bit to be cleared in MIND

Reported-by: Alexandre Messier <amessier@tycoint.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Tested-by: Alexandre Messier <amessier@tycoint.com>