misc: fastrpc: fix use-after-free race in fastrpc_map_create

In the Linux kernel, the following vulnerability has been resolved:

misc: fastrpc: fix use-after-free race in fastrpc_map_create

fastrpc_map_lookup returns a raw pointer after releasing fl->lock. The

caller fastrpc_map_create then calls fastrpc_map_get (kref_get_unless_zero)

on this unprotected pointer. A concurrent MEM_UNMAP can free the map

between the lock release and the kref operation, resulting in a

use-after-free on the freed slab object.

Restore the take_ref parameter to fastrpc_map_lookup so the reference

is acquired atomically under fl->lock before the pointer is exposed to

the caller.