When running a stress playback/stop loop test on a mx6wandboard channel
swaps can be noticed randomly.

Increasing the SGTL5000 LRCLK pad strength to its maximum value fixes
the issue, so add the 'lrclk-strength' property to avoid the audio
channel swaps.
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>