This definition missing from <linux/major.h> for kernels <= 3.13.

Signed-off-by: Alex Suykov <alex.suykov@gmail.com>

--- a/cgpt/cgpt_wrapper.c
+++ b/cgpt/cgpt_wrapper.c
@@ -25,6 +25,10 @@
 #include "cgpt_nor.h"
 #include "cryptolib.h"
 
+#ifndef MTD_CHAR_MAJOR
+#define MTD_CHAR_MAJOR 90
+#endif
+
 // Check if cmdline |argv| has "-D". "-D" signifies that GPT structs are stored
 // off device, and hence we should not wrap around cgpt.
 static bool has_dash_D(int argc, const char *const argv[]) {