media: v4l: ioctl: Use kmalloc to allocate a small chunk of memory

kvmalloc() was used to allocate the temporary memory buffer that was used
to contain both the IOCTL argument as well as a possible array argument
that could have been large. Now that the two are separated, the IOCTL
argument is known to be small in size. Use kmalloc to allocate it instead
of kvmalloc. Similarly for releasing it.

Suggested-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>