return early from drm activate functions after fatal error

return early from drm activate functions after fatal error

avoids a page fault trap trying to take an uninitialised
modeset lock on suspend

reported and tested by Ali Farzanrad on HP ProBook 4530s

radeondrm0 at pci1 dev 0 function 0 "ATI Radeon HD 6400M" rev 0x00
drm1 at radeondrm0
radeondrm0: msi
inteldrm0 at pci0 dev 2 function 0 "Intel HD Graphics 3000" rev 0x09
drm0 at inteldrm0
inteldrm0: msi, SANDYBRIDGE, gen 6
..
radeondrm0: CAICOS
[drm] *ERROR* Unable to locate a BIOS ROM
drm:pid0:radeondrm_attachhook *ERROR* Fatal error during GPU init
inteldrm0: 1366x768, 32bpp