drm/nouveau/kms/nv50-: Correct size checks for cursors

Found this while trying to make some changes to the kms_cursor_crc test.
curs507a_acquire checks that the width and height of the cursor framebuffer
are equal (asyw->image.{w,h}). This isn't entirely correct though, as the
height of the cursor can be larger than the size of the cursor, as long as
the width is the same as the cursor size and there's no framebuffer offset.

Note that I'm not entirely sure why this wasn't previously breaking
kms_cursor_crc tests - they all set up cursors with the height being one
pixel larger than the actual size of the cursor. But this seems to fix
things, and the code before was definitely incorrect - so it's not really
worth looking into further imho.

Changes since v1:
* Don't use crtc_w everywhere for determining cursor layout, just use fb
  size again
* Change check so that we only check that the w/h of the cursor plane is
  the same, the width of the scanout surface is the same as the framebuffer
  width, and that there's no offset being used for the cursor surface.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Martin Peres <martin.peres@mupuf.org>
Cc: Jeremy Cline <jcline@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10