Build fails with FATFS_INC_LFN_SUPPORT=0

[mickjc750]

fat_write.c:(.text+0x255): undefined reference to `fatfs_entry_lfn_text'

fatfs_entry_lfn_text() is still called at fat_write.c:160 even though DFATFS_INC_LFN_SUPPORT=0 and the code for fatfs_entry_lfn_text() is not compiled.