Staging: sm750fb: Remove unused functions

The functions dviGetDeviceID and dviGetVendorID are not used anywhere in
the kernel so remove them. Also, remove their function prototypes.
Grepped to find occurences.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>