sandbox: Add missing errno.h includes in a few files

These files use error numbering, so add the include.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/start.c

@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <errno.h>
 #include <os.h>
 #include <cli.h>
 #include <malloc.h>

drivers/misc/i2c_eeprom_emul.c

@@ -8,6 +8,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <errno.h>
 #include <fdtdec.h>
 #include <i2c.h>
 #include <malloc.h>

drivers/misc/swap_case.c

@@ -9,6 +9,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <errno.h>
 #include <pci.h>
 #include <asm/test.h>
 #include <linux/ctype.h>