mtd: nane: print source of error message

Add the function name to the error message.

These messages are not very helpful:

[183356.176682] uncorrectable error :
[183356.180273] uncorrectable error :
[183356.184194] uncorrectable error :
[183356.187773] uncorrectable error :
[183356.191280] uncorrectable error :

Artem: amended the patch a bit

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>