drm: imx: fix compiler warning with gcc-12

Gcc-12 correctly warned about this code using a non-NULL pointer as a
truth value:

  drivers/gpu/drm/imx/ipuv3-crtc.c: In function ‘ipu_crtc_disable_planes’:
  drivers/gpu/drm/imx/ipuv3-crtc.c:72:21: error: the comparison will always evaluate as ‘true’ for the address of ‘plane’ will never be NULL [-Werror=address]
     72 |                 if (&ipu_crtc->plane[1] && plane == &ipu_crtc->plane[1]->base)
        |                     ^

due to the extraneous '&' address-of operator.

Philipp Zabel points out that The mistake had no adverse effect since
the following condition doesn't actually dereference the NULL pointer,
but the intent of the code was obviously to check for it, not to take
the address of the member.

Fixes: eb8c8880

 ("drm/imx: add deferred plane disabling")
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>