staging: sm750fb: Removes unused variable from sm750_hw_copyarea

Removes unused variable opSign from sm750_hw_copyarea. Identified
using coccinelle script 'unused.cocci'.

Signed-off-by: Tahia Khan <tahia.khan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>