ASoC: imx-audmux: Use uintptr_t for port numbers

Since we pass the port number through file private data for debugfs we cast
it to and from a pointer so use uintptr_t in order to ensure that the
types are compatible, avoiding warnings on 64 bit platforms where pointers
are 64 bit and unsigned integers 32 bit.

Signed-off-by: Mark Brown <broonie@linaro.org>