[radeon] radeon_kick_out_firmware_fb() can deref NULL

[Sylvain 'ythier' Hitier]

Hello,

In commit a56f7428d7534f162fbb089c5c79012bf38a7c29 [1], the result of
alloc_apertures() function call is used without checking for a possible NULL
result, which may happen, as seen in [2].

The latest commit [3] in the drm-fixes branch of the
linux/kernel/git/airlied/drm-2.6.git repo still has the issue.

[1] http://git.kernel.org/?p=linux/kernel/git/airlied/drm-2.6.git;a=commitdiff;h=a56f7428d7534f162fbb089c5c79012bf38a7c29
[2] http://git.kernel.org/?p=linux/kernel/git/airlied/drm-2.6.git;hb=refs/heads/drm-fixes;a=blob;f=include/linux/fb.h#l890
[3] http://git.kernel.org/?p=linux/kernel/git/airlied/drm-2.6.git;a=commit;h=d15eda5c6edff4987af6f4423af0bab0c3251e74

Regards,
Sylvain "ythier" Hitier

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