ARM: OMAP2+: Fix -Warray-bounds warning in _pwrdm_state_switch()

If function pwrdm_read_prev_pwrst() returns -EINVAL, we will end
up accessing array pwrdm->state_counter through negative index
-22. This is wrong and the compiler is legitimately warning us
about this potential problem.

Fix this by sanity checking the value stored in variable _prev_
before accessing array pwrdm->state_counter.

Address the following -Warray-bounds warning:
arch/arm/mach-omap2/powerdomain.c:178:45: warning: array subscript -22 is below array bounds of 'unsigned int[4]' [-Warray-bounds]

Link: https://github.com/KSPP/linux/issues/307
Fixes: ba20bb12 ("OMAP: PM counter infrastructure.")
Cc: stable@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/20230607050639.LzbPn%25lkp@intel.com/Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Message-ID: <ZIFVGwImU3kpaGeH@work>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/powerdomain.c

@@ -174,7 +174,7 @@ static int _pwrdm_state_switch(struct powerdomain *pwrdm, int flag)
 		break;
 	case PWRDM_STATE_PREV:
 		prev = pwrdm_read_prev_pwrst(pwrdm);
-		if (pwrdm->state != prev)
+		if (prev >= 0 && pwrdm->state != prev)
 			pwrdm->state_counter[prev]++;
 		if (prev == PWRDM_POWER_RET)
 			_update_logic_membank_counters(pwrdm);