powerpc64: Remove unused variables avoid gcc warnings

[breno.leitao_gmail.com]

Summary

Compiling the powerpc64 kernel with a newer GCC generates some annoying
messages, as unused and uninitialized variables.

This patchset fixes these warnings and this patchset shouldn't cause any change
in the code.

[jhibbits]

sys/powerpc/cpufreq/pmufreq.c

117

This line can just be deleted.

sys/powerpc/pseries/phyp_llan.c

159

I think this is incorrect, and error should be handled.

187

Don't ignore it, handle it.

285

Error should be handled, not ignored.

[breno.leitao_gmail.com]

Resubmitting a code that treats the errors other than ignoring them,.

[jhibbits]

sys/powerpc/pseries/phyp_llan.c

194

You need to clean up the resource allocations when you exit prematurely. Often there'll be a label at the end of the function to do cleanup before returning error.

304

Is there any cleanup needed from the H_FREE_LOGICAL_LAN call if this second hcall fails?