clk: versatile: Improve sizeof() usage

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.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>