Adjust Requires for modules-extra pacakge to rely on kernel-uname-r
The variant kernels (e.g. PAE) Provide kernel-%{_target_cpu}, which doesn't
include the variant name so we wind up with broken deps on the modules-extra
subpackage. kernel-uname-r incorporates the variant value at the end (e.g.
kernel-uname-r = 3.2.0-0.rc4.git0.2.fc17.i686.PAE)