ARM: pxa: Improve a size determination in pxa3xx_u2d_probe()

Replace the specification of a data structure by a pointer dereference
as the parameter for the operator "sizeof" to make the corresponding size
determination a bit safer according to the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>