staging: wilc1000: use ENOBUFS error code instead of WILC_TX_ERR_NO_BUF macro

Make use of 'ENOBUFS' instead of WILC_TX_ERR_NO_BUF macro. The value of
WILC_TX_ERR_NO_BUF is -2, which is confusing with ENOENT error code.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>