ASoC: mpc5200_psc_i2s: Fix invalid license ID

As the file had no other license notice/reference, it falls under the
project license and therefore the proper SPDX id is: GPL-2.0-only

Cc: Daniel Baluta <daniel.baluta@nxp.com>
Fixes: 864a8472 ("ASoC: mpc5200_psc_i2s: Switch to SPDX identifier")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andra Danciu <andradanciu1997@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>