ARM: dts: da850-evm: Correct the sound card name

To avoid  the following error:
asoc-simple-card sound: ASoC: Failed to create card debugfs directory

Which is because the card name contains '/' character, which can not be
used in file or directory names.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>