fbdev: omapfb: lcd_mipid: Fix an error handling path in mipid_spi_probe()

If 'mipid_detect()' fails, we must free 'md' to avoid a memory leak.

Fixes: 66d2f99d ("omapfb: add support for MIPI-DCS compatible LCDs")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Helge Deller <deller@gmx.de>