Fix condition for calling set_pixmap_bo in drmmode_xf86crtc_resize

This matches CreateScreenResources_KMS.

Fixes crash when resizing the screen (e.g. using xrandr) with depth <
24.

Bugzilla: https://bugs.freedesktop.org/104914
Acked-by: Alex Deucher <alexander.deucher@amd.com>
11 jobs for depth-16-randr-crash in 4 minutes and 14 seconds (queued for 1 minute and 6 seconds)
Status Job ID Name Coverage
  Build
passed #28464
xserver-1.13

00:00:36

passed #28465
xserver-1.14

00:00:40

passed #28466
xserver-1.15

00:00:41

passed #28467
xserver-1.16

00:00:40

passed #28468
xserver-1.17

00:00:39

passed #28469
xserver-1.18

00:00:38

passed #28470
xserver-1.18-clang

00:00:42

passed #28471
xserver-1.19

00:00:38

passed #28472
xserver-1.19-clang

00:00:38

passed #28462
xserver-1.20

00:00:57

passed #28463
xserver-1.20-clang

00:00:40