um: syscall.c: include <asm/unistd.h>

Without CONFIG_SECCOMP, we don't get this include recursively
through the existing includes, thus failing the build on not
having __NR_syscall_max defined. Add the necessary include to
fix this.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/kernel/skas/syscall.c

@@ -11,6 +11,7 @@
 #include <sysdep/ptrace_user.h>
 #include <sysdep/syscalls.h>
 #include <linux/time-internal.h>
+#include <asm/unistd.h>
 
 void handle_syscall(struct uml_pt_regs *r)
 {