staging: sm750fb: use tabs for indentation

Replace spaces with tabs for indentation to fix the checkpatch.pl error
ERROR: code indent should use tabs where possible
WARNING: please, no spaces at the start of a line

Signed-off-by: Juston Li <juston.h.li@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>