media: uvcvideo: Use parentheses around sizeof operand

While the sizeof is an operator and not a function, the preferred coding
style in the kernel is to enclose its operand in parentheses. To avoid
mixing multiple coding styles in the driver, use parentheses around all
sizeof operands.

While at it replace a kmalloc() with a kmalloc_array() to silence a
checkpatch warning triggered by this patch.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>