media: gspca_kinect: cast sizeof to int for comparison

Comparing an int to a size, which is unsigned, causes the int to become
unsigned, giving the wrong result.  kinect_read returns the result of
usb_control_msg, which can return a negtive error code.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/

)

// <smpl>
@@
int x;
expression e,e1;
identifier f;
@@

*x = f(...);
... when != x = e1
    when != if (x < 0 || ...) { ... return ...; }
*x < sizeof(e)
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>