USB: ftdi-elan.c: fixes and cleanups

This patch contains the following possible cleanups:
- make the needlessly global ftdi_release_platform_dev() static
- remove the unused usb_ftdi_elan_read_reg()
- proper prototypes for the following functions:
  - usb_ftdi_elan_read_pcimem()
  - usb_ftdi_elan_write_pcimem()

Note that the misplaced prototypes for the latter ones in
drivers/usb/host/u132-hcd.c were buggy. Depending on the calling
convention of the architecture calling one of them could have turned
your stack into garbage.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>