Input: bu21013_ts - request regulator that actually exists

Currently the BU21013 Touch Screen driver requests a regulator by the
name of 'V-TOUCH', which doesn't exist anywhere in the kernel. The
correct name, as referenced in platform regulator code is 'avdd'. Here,
when we request a regulator, we use the correct name instead.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>