lcd: Fix BMP decode bug that skips the wrong padded row

This change fixed 2 things:
 - Rename padded_line to padded_width since it is (width + padded_row) not line.
 - When finished a line, should skip the padded_row that is
   (padded_width - width) instead of (width - padded_width).

Reference: http://en.wikipedia.org/wiki/BMP_file_format


Signed-off-by: Tom Wai-Hong Tam <waihong@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>