[UBI] - Interval tree fixes

Fixed interval tree implementation.
[UBI] - Interval tree dump

Added a dump utility to display interval tree content
(using printk calls)
[UBI][HMAC] - Fix

Fixed an issue in ubi_crypto_compute_hmac_hdr
[UBI][HMAC] - Miscellaneous fixes

Fixes include :
-> A memory leak correction
-> Programming mistakes
[UBI][HMAC] - Bug fixes

The eba sub-system was able to return IO sub-system error codes,
which are greater than 0. UBIFS would treat them as valid pointers
and this would cause a page fault.
This is now fixed.

On the other hand, HMAC header primitives were revised.