memory: stm32_omm: Fix req2ack update test

If "st,omm-req2ack-ns" property is found and its value is not 0,
the current test doesn't allow to compute and set req2ack value,
Fix this test.

Fixes: 8181d061dcff ("memory: Add STM32 Octo Memory Manager driver")
Signed-off-by: Patrice Chotard <[e-mail]>
Link: https://lore.kernel.org/r/20[e-mail]
Cc: <[e-mail]>
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

drivers/memory/stm32_omm.c

···
 		if (mux & CR_MUXEN) {
 			ret = of_property_read_u32(dev->of_node, "st,omm-req2ack-ns",
 						   &req2ack);
-			if (!ret && !req2ack) {
+			if (!ret && req2ack) {
 				req2ack = DIV_ROUND_UP(req2ack, NSEC_PER_SEC / clk_rate_max) - 1;
 
 				if (req2ack > 256)