Compiling the 'bmp' command with DM and having one of the following macros
enabled:

CONFIG_BMP_16BPP, CONFIG_BMP_24BPP ONFIG_BMP_32BPP

generates this error:

drivers/video/video_bmp.c: In function ‘video_bmp_display’:
drivers/video/video_bmp.c:315:22: error: ‘lcd_line_length’ undeclared (first use in this function)
    fb -= width * 2 + lcd_line_length;
                          ^

This patch moves to using the correct variable instead and enables the
'bmp' command for DM again.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Anatolij Gustschin <agust@denx.de>