powerpc/perf/hv-24x7: Make some symbols static

The sparse tool complains as follows:

arch/powerpc/perf/hv-24x7.c:229:1: warning:
 symbol '__pcpu_scope_hv_24x7_txn_flags' was not declared. Should it be static?
arch/powerpc/perf/hv-24x7.c:230:1: warning:
 symbol '__pcpu_scope_hv_24x7_txn_err' was not declared. Should it be static?
arch/powerpc/perf/hv-24x7.c:236:1: warning:
 symbol '__pcpu_scope_hv_24x7_hw' was not declared. Should it be static?
arch/powerpc/perf/hv-24x7.c:244:1: warning:
 symbol '__pcpu_scope_hv_24x7_reqb' was not declared. Should it be static?
arch/powerpc/perf/hv-24x7.c:245:1: warning:
 symbol '__pcpu_scope_hv_24x7_resb' was not declared. Should it be static?

This symbol is not used outside of hv-24x7.c, so this
commit marks it static.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Bixuan Cui <cuibixuan@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210409090124.59492-1-cuibixuan@huawei.com