tosa_battery: Fix build error due to direct driver_data usage

The driver isn't buildable since 2.6.32 (i.e. commit b4028437
"Driver core: move dev_get/set_drvdata to drivers/base/dd.c"):

  CC      tosa_battery.o
tosa_battery.c: In function 'tosa_read_bat':
tosa_battery.c:64: error: 'struct device' has no member named 'driver_data'
tosa_battery.c: In function 'tosa_read_temp':
tosa_battery.c:84: error: 'struct device' has no member named 'driver_data'

Nowadays we must not access driver_data directly, use dev_get_drvdata()
instead.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>