spl: fit: Fix non-matching DT names console output

When no DTB can be matched successfully to the board that's being used
a list of available FIT-embedded DTBs will be output to the console for
diagnostic purposes. But rather than the contents of the "description"
FDT property a non-existent property was accessed and as a result "NULL"
was output instead of the actual name(s) of the DTB(s). Fix this issue
by using the correct property which is also the exact same property
that's used earlier during the actual board matching process.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>