mtd: mtd_oobtest: Show the verification error location and data

Add a function memcmpshow() that compares the 2 data buffers
and shows the address:offset and data bytes on comparison failure.
This function  does not break at a comparison failure but runs the
check for the whole data buffer.

Use memcmpshow() instead of memcmp() for all the verification paths.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>