video/smscufx: fix line counting in fb_write

commit 2fe2d9f4 upstream.

Line 0 and 1 were both written to line 0 (on the display) and all subsequent
lines had an offset of -1. The result was that the last line on the display
was never overwritten by writes to /dev/fbN.

The origin of this bug seems to have been udlfb.
Signed-off-by: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/video/smscufx.c

@@ -904,7 +904,7 @@ static ssize_t ufx_ops_write(struct fb_info *info, const char __user *buf,
 	result = fb_sys_write(info, buf, count, ppos);
 
 	if (result > 0) {
-		int start = max((int)(offset / info->fix.line_length) - 1, 0);
+		int start = max((int)(offset / info->fix.line_length), 0);
 		int lines = min((u32)((result / info->fix.line_length) + 1),
 				(u32)info->var.yres);