mmc: dw_mmc-bluefield: : Fix the license information

The SPDX license identifier and the boiler plate text are
contradicting. Only the SPDX license identifier is needed. The
other one is removed.

Fixes: 86958dcc

 ("mmc: dw_mmc-bluefield: Add driver extension")
Cc: stable@vger.kernel.org
Reviewed-by: David Woods <dwoods@mellanox.com>
Signed-off-by: Liming Sun <lsun@mellanox.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>