flash: nor: stm32f2x: add NULL check for stm32x_info

This commit prevents NULL dereference during malloc
failure on stm32x bank command.

Change-Id: Ib348a1863aee5f8ed9d1699d203cdc4c83557628
Signed-off-by: Igor Cudnik <igor@its.rel.pl>
Reviewed-on: https://review.openocd.org/c/openocd/+/9379
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins

src/flash/nor/stm32f2x.c

@@ -250,6 +250,10 @@ FLASH_BANK_COMMAND_HANDLER(stm32x_flash_bank_command)
 		return ERROR_COMMAND_SYNTAX_ERROR;
 
 	stm32x_info = malloc(sizeof(struct stm32x_flash_bank));
+	if (!stm32x_info) {
+		LOG_ERROR("Out of memory");
+		return ERROR_FAIL;
+	}
 	bank->driver_priv = stm32x_info;
 
 	stm32x_info->probed = false;