ati_radeon: return with error when emulator fails

Console was being switched to video even if emulator fails and
causing this hang:

               Scanning PCI bus 04
        04  00  1095  3132  0104  00
    PCIE3 on bus 03 - 04
Video: ATI Radeon video card (1002, 5b60) found @(2:0:0)
videoboot: Booting PCI video card bus 2, function 0, device 0
videoboot: Video ROM failed to map!
640x480x8 31kHz 59Hz
radeonfb: FIFO Timeout !

Signed-off-by: Ed Swarthout <Ed.Swarthout@freescale.com>
Tested-by: Anatolij Gustschin <agust@denx.de>