fbdev: sh_mobile_lcdc: Update fix.line_length in .fb_set_par()

Instead of updating the fixed screen information line length manually
after calling fb_set_var() in sh_mobile_fb_reconfig(), update the field
in the .fb_set_par() operation handler.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>