spi: Add <errno.h> to spi-mem-nodm.c

This file uses errno return values in functions, so include <errno.h>
here rather than rely on indirect inclusion.

Signed-off-by: Tom Rini <trini@konsulko.com>

drivers/spi/spi-mem-nodm.c

@@ -3,6 +3,7 @@
  * Copyright (C) 2018 Texas Instruments Incorporated - http://www.ti.com/
  */
 
+#include <errno.h>
 #include <log.h>
 #include <malloc.h>
 #include <spi.h>