ASoC: fsl_ssi: Use 'const _be *' type for iprop

ASoC: fsl_ssi: Use 'const _be *' type for iprop

The 'iprop' variable is passed as an argument to the be32_to_cpup()
function, which expects a 'const _be *' type.

Change the iprop variable type so that the following build warnings
with W=1 are gone:

sound/soc/fsl/fsl_ssi.c:1463:48: warning: incorrect type in argument 1 (different base types)
sound/soc/fsl/fsl_ssi.c:1463:48:    expected restricted __be32 const [usertype] *p
sound/soc/fsl/fsl_ssi.c:1463:48:    got unsigned int const [usertype] *[assigned] iprop

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>