Documentation: USB: correct possessive "its" usage

Correct uses of "it's" to possessive "its" or "its" to "it's" as needed.
Correct associated grammar in one location.

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/usb/CREDITS

···
 Credits for the Simple Linux USB Driver:
 
 The following people have contributed to this code (in alphabetical
-order by last name).  I'm sure this list should be longer, its
+order by last name).  I'm sure this list should be longer, it's
 difficult to maintain, add yourself with a patch if desired.
 
   Georg Acher <[e-mail]>
···
         - Jochen Karrer <[e-mail]>, for
           pointing out mortal bugs and giving advice.
 
-        - Edmund Humemberger <[e-mail]>, for it's great work on
+        - Edmund Humemberger <[e-mail]>, for his great work on
           public relationships and general management stuff for the
           Linux-USB effort.
 
···
         - Ric Klaren <[e-mail]> for doing nice
           introductory documents (competing with Alberto's :).
 
-        - Christian Groessler <[e-mail]>, for it's help on those
+        - Christian Groessler <[e-mail]>, for his help on those
           itchy bits ... :)
 
         - Paul MacKerras for polishing OHCI and pushing me harder for

Documentation/usb/functionfs.rst

···
   $ ( cd /dev/ffs-hid && hid-daemon ) &
 
 On kernel level the gadget checks ffs_data->dev_name to identify
-whether it's FunctionFS designed for MTP ("mtp") or HID ("hid").
+whether its FunctionFS is designed for MTP ("mtp") or HID ("hid").
 
 If no "functions" module parameters is supplied, the driver accepts
 just one function with any name.

Documentation/usb/gadget_multi.rst

···
 that makes extensive use of the composite framework to provide
 a... multifunction gadget.
 
-In it's standard configuration it provides a single USB configuration
+In its standard configuration it provides a single USB configuration
 with RNDIS[1] (that is Ethernet), USB CDC[2] ACM (that is serial) and
 USB Mass Storage functions.