binder: Remove incorrect comment about vm_insert_page() behavior

binder: Remove incorrect comment about vm_insert_page() behavior

vm_insert_page() does increment the page refcount, and just to be sure,
I've confirmed it by printing page_count(page[0].page_ptr) before and after
vm_insert_page(). It's 1 before, 2 afterwards, as expected.

Fixes: a145dd411eb2 ("VM: add "vm_insert_page()" function")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191018153946.128584-1-jannh@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>