rtl8192u: Don't use create_proc_read_entry()

Don't use create_proc_read_entry() as that is deprecated, but rather use
proc_create_data() and seq_file instead.  Whilst we're at it, reduce the
number of show functions where we can share them.

Note: proc_get_stats_ap() should probably use seq_file iteration rather than
list_for_each_entry().

Further note: There appears to be a lot of locking missing in this file to
defend against concurrent access by the driver doing normal operations.
Notably, ieee->network_list traversal and RWCAM/RCAMO command/response access.
Further, do any of the registers read have side effects upon reading?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jerry Chuang <jerry-chuang@realtek.com>
cc: Mauro Carvalho Chehab <mchehab@redhat.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: linux-wireless@vger.kernel.org
cc: devel@driverdev.osuosl.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>