ASoC: imx: imx-audmux: Fix section mismatch

Fix the following section mismatch warning:

WARNING: vmlinux.o(.data+0x35be8): Section mismatch in reference from the variable imx_audmux_driver to the function .init.text:imx_audmux_probe()
The variable imx_audmux_driver references
the function __init imx_audmux_probe()
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>