staging: bcm2835-camera: prefer allocating memory using sizeof(*ptr) instead...

staging: bcm2835-camera: prefer allocating memory using sizeof(*ptr) instead of sizeof(struct type name)

Using sizeof(*ptr) instead of sizeof(struct type name) is more robust to
errors.

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>