mfd: db8500-prcmu: Supply the pdata_size attribute for db8500-thermal

The MFD subsystem requires drivers to state the size of any platform
data passed, or it will fail to assign it to the device. This will
culminate in a NULL platform_data attribute and normally a failure to
probe() or a kernel Oops.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>