xf86drm: Fix segmentation fault while parsing device info

This fixes a bug, which was introduced with commit ee798b98
"xf85drm: de-duplicate drmParse{Platform.Host1x}{Bus,Device}Info".
where accessing *compatible[i] with i>0 results in a segfault.

Signed-off-by: Andreas Baierl <ichgeh@imkreisrum.de>
Fixes: ee798b98 "xf85drm: de-duplicate drmParse{Platform.Host1x}{Bus,Device}Info"
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
[Eric: add the same fix to the free() below]
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>