of: fix implicit use of errno.h in include/linux/of.h

It shows up as a build failure on MIPS, as it is used in
three of_property function stubs.

include/linux/of.h:275: error: 'ENOSYS' undeclared (first use in this function)
include/linux/of.h:282: error: 'ENOSYS' undeclared (first use in this function)
include/linux/of.h:295: error: 'ENOSYS' undeclared (first use in this function)
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

include/linux/of.h

@@ -23,6 +23,7 @@
 #include <linux/spinlock.h>
 
 #include <asm/byteorder.h>
+#include <asm/errno.h>
 
 typedef u32 phandle;
 typedef u32 ihandle;