drm/tegra: Fix another missing include

Since Tegra now compile tests on other platforms the kernel test robot
started to complain that this here is not pulled in under all
conditions.

Signed-off-by: Christian König <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Link: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/drm/tegra/fb.c

···
  */
 
 #include <linux/console.h>
+#include <linux/vmalloc.h>
 
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>