video: hyperv_fb: include vmalloc.h

hvfb_getmem uses vzalloc, therefore vmalloc.h should be included.

Fixes commit d21987d7 ("video: hyperv:
hyperv_fb: Support deferred IO for Hyper-V frame buffer driver")
Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106183941.9751-1-olaf@aepfle.de

drivers/video/fbdev/hyperv_fb.c

@@ -47,6 +47,7 @@
 
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/completion.h>
 #include <linux/fb.h>