Fix up incorrect usage of sizeof

In
void whatever(u8 x[20])
sizeof(x) returns the size of a u8* pointer, not (as the code
here would expect) 20...

Change-Id: I5a96b2648499f7203b8cc7666849ff80d0019c2d
Signed-off-by: Bernhard Rosenkränzer <bernhard.rosenkranzer@linaro.org>