docs: networking: phy: Rephrase paragraph for clarity

Let's make it a little easier to read.

Signed-off-by: Jonathan Neuschäfer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/networking/phy.rst

···
 The stubs set one of the two matching criteria, and set the other one to
 match anything.
 
-When phy_register_fixup() or \*_for_uid()/\*_for_id() is called at module,
-unregister fixup and free allocate memory are required.
+When phy_register_fixup() or \*_for_uid()/\*_for_id() is called at module load
+time, the module needs to unregister the fixup and free allocated memory when
+it's unloaded.
 
 Call one of following function before unloading module::