fpga: bridge: add owner module and take its refcount

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

fpga: bridge: add owner module and take its refcount

The current implementation of the fpga bridge assumes that the low-level

module registers a driver for the parent device and uses its owner pointer

to take the module's refcount. This approach is problematic since it can

lead to a null pointer dereference while attempting to get the bridge if

the parent device does not have a driver.

To address this problem, add a module owner pointer to the fpga_bridge

struct and use it to take the module's refcount. Modify the function for

registering a bridge to take an additional owner module parameter and

rename it to avoid conflicts. Use the old function name for a helper macro

that automatically sets the module that registers the bridge as the owner.

This ensures compatibility with existing low-level control modules and

reduces the chances of registering a bridge without setting the owner.

Also, update the documentation to keep it consistent with the new interface

for registering an fpga bridge.

Other changes: opportunistically move put_device() from __fpga_bridge_get()

to fpga_bridge_get() and of_fpga_bridge_get() to improve code clarity since

the bridge device is taken in these functions.