ARM: vexpress/spc: Avoid negative array index when !SMP

ARM: vexpress/spc: Avoid negative array index when !SMP

When building multi_v7_defconfig+CONFIG_SMP=n, -Warray-bounds exposes
a couple negative array index accesses:

arch/arm/mach-vexpress/spc.c: In function 've_spc_clk_init':
arch/arm/mach-vexpress/spc.c:583:21: warning: array subscript -1 is below array bounds of 'bool[2]' {aka '_Bool[2]'} [-Warray-bounds]
  583 |   if (init_opp_table[cluster])
      |       ~~~~~~~~~~~~~~^~~~~~~~~
arch/arm/mach-vexpress/spc.c:556:7: note: while referencing 'init_opp_table'
  556 |  bool init_opp_table[MAX_CLUSTERS] = { false };
      |       ^~~~~~~~~~~~~~
arch/arm/mach-vexpress/spc.c:592:18: warning: array subscript -1 is below array bounds of 'bool[2]' {aka '_Bool[2]'} [-Warray-bounds]
  592 |    init_opp_table[cluster] = true;
      |    ~~~~~~~~~~~~~~^~~~~~~~~
arch/arm/mach-vexpress/spc.c:556:7: note: while referencing 'init_opp_table'
  556 |  bool init_opp_table[MAX_CLUSTERS] = { false };
      |       ^~~~~~~~~~~~~~

Skip this logic when built !SMP.

Link: https://lore.kernel.org/r/20220331190443.851661-1-keescook@chromium.org
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>