binder: fix sparse issue in binder_alloc_selftest.c

Fixes sparse issues reported by the kbuild test robot running
on https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
char-misc-testing: bde4a19fc04f5 ("binder: use userspace pointer as base
of buffer space")

Error output (drivers/android/binder_alloc_selftest.c):
sparse: warning: incorrect type in assignment (different address spaces)
sparse: expected void *page_addr
sparse: got void [noderef] <asn:1> *user_data
sparse: error: subtraction of different types can't work

Fixed by adding necessary "__user" tags.

Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Todd Kjos <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/android/binder_alloc_selftest.c

···
 					 struct binder_buffer *buffer,
 					 size_t size)
 {
-	void *page_addr, *end;
+	void __user *page_addr;
+	void __user *end;
 	int page_index;
 
-	end = (void *)PAGE_ALIGN((uintptr_t)buffer->user_data + size);
+	end = (void __user *)PAGE_ALIGN((uintptr_t)buffer->user_data + size);
 	page_addr = buffer->user_data;
 	for (; page_addr < end; page_addr += PAGE_SIZE) {
 		page_index = (page_addr - alloc->buffer) / PAGE_SIZE;