android: binder: fix binder mmap failures

binder_update_page_range() initializes only addr and size
fields in 'struct vm_struct tmp_area;' and passes it to
map_vm_area().

Before 71394fe5 ("mm: vmalloc: add flag preventing guard hole allocation")
this was because map_vm_area() didn't use any other fields
in vm_struct except addr and size.

Now get_vm_area_size() (used in map_vm_area()) reads vm_struct's
flags to determine whether vm area has guard hole or not.

binder_update_page_range() don't initialize flags field, so
this causes following binder mmap failures:
-----------[ cut here ]------------
WARNING: CPU: 0 PID: 1971 at mm/vmalloc.c:130
vmap_page_range_noflush+0x119/0x144()
CPU: 0 PID: 1971 Comm: healthd Not tainted 4.0.0-rc1-00399-g7da3fdc-dirty #157
Hardware name: ARM-Versatile Express
[<c001246d>] (unwind_backtrace) from [<c000f7f9>] (show_stack+0x11/0x14)
[<c000f7f9>] (show_stack) from [<c049a221>] (dump_stack+0x59/0x7c)
[<c049a221>] (dump_stack) from [<c001cf21>] (warn_slowpath_common+0x55...