Fix a mistaken conditional in mfi_tbolt_send_frame()

As written, the condition of (cdb[0] != 0x28 || cdb[0] != 0x2A) will always
be true, since if it's one, it's obviously not the other. Reading the code,
the intent appears to be that it should only perform the operation if it's
neither, otherwise the conditional can be elided.

Found by clang 10.