Enable further warning flags, address new warnings

Enable further warning flags, address new warnings

mtd_debug: Remove a duplicate if case. MTD_CAP_NANDFLASH has only one
flag set (MTD_WRITEABLE). Directly below, we had a check for
MTD_WRITEABLE in the else branch which can't possible ever have
triggered. Checking for MTD_WRITEABLE in addition to the CAP constants
was probably not intended anyway, given the check for the individual
flags if all else fails.

integck: We already established that "r" is less than the number of
elements in the list, so the loop condition doesn't need to check
if w is NULL in addition. At least this way, the compiler "gets"
that w cannot be NULL below and doesn't issue warnings.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>