powerpc/xive: fix repeated words in comments

Delete the redundant word 'set'.

Signed-off-by: Jilin Yuan <yuanjilin@cdjrlc.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220831004706.35280-1-yuanjilin@cdjrlc.com