mm/process_vm_access.c: include compat.h

Fix the build error:

  mm/process_vm_access.c:277:5: error: implicit declaration of function 'in_compat_syscall'; did you mean 'in_ia32_syscall'? [-Werror=implicit-function-declaration]

Fixes: 38dc507 "Fix compat regression in process_vm_rw()"
Reported-by: [email protected]
Cc: Kyle Huey <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/process_vm_access.c

@@ -9,6 +9,7 @@
 #include <linux/mm.h>
 #include <linux/uio.h>
 #include <linux/sched.h>
+#include <linux/compat.h>
 #include <linux/sched/mm.h>
 #include <linux/highmem.h>
 #include <linux/ptrace.h>