ARM: ux500: Fix merge error, no matching driver name for 'snd_soc_u8500'

The platform attempts to register platform device 'snd_soc_u8500'
which doesn't actually exist. Here we change the reference to the
correct one 'snd_soc_mop500'.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>