powerpc/powernv: Remove unneeded variable: "rc"

Remove unneeded variable: "rc".

Signed-off-by: dingsenjie <dingsenjie@yulong.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210326115356.12444-1-dingsenjie@163.com