drm: remove the newline for CRC source name.

userspace may transfer a newline, and this terminating newline
is replaced by a '\0' to avoid followup issues.

'len-1' is the index to replace the newline of CRC source name.

v3: typo fix (Sam)

v2: update patch subject, body and format. (Sam)

Cc: Leo Li <sunpeng.li@amd.com>
Cc: Harry Wentland <Harry.Wentland@amd.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Dingchen Zhang <dingchen.zhang@amd.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190610134751.14356-1-dingchen.zhang@amd.com

drivers/gpu/drm/drm_debugfs_crc.c

@@ -140,8 +140,8 @@ static ssize_t crc_control_write(struct file *file, const char __user *ubuf,
 	if (IS_ERR(source))
 		return PTR_ERR(source);
 
-	if (source[len] == '\n')
-		source[len] = '\0';
+	if (source[len - 1] == '\n')
+		source[len - 1] = '\0';
 
 	ret = crtc->funcs->verify_crc_source(crtc, source, &values_cnt);
 	if (ret)