staging: sm750fb: remove proc_checkMode method from lynxfb_output

The proc_checkMode of lynxfb_output is set to function that always
returns 0. Calling that function and checking for its return value is
meaningless.

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>