um: Add asm/elf.h to vma.c

um_vdso_addr is defined in asm/elf.h.
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/vdso/vma.c

@@ -10,6 +10,7 @@
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <asm/page.h>
+#include <asm/elf.h>
 #include <linux/init.h>
 
 static unsigned int __read_mostly vdso_enabled = 1;