usbd: remove compiler warnings

usbd: remove compiler warnings

cmd_usbd.c: In function 'write_fat_file':
cmd_usbd.c:745: warning: passing argument 2 of 'file_fat_write' makes pointer from integer without a cast
/home/share/Work/u-boot-merge/include/fat.h:220: note: expected 'void *' but argument is of type 'long unsigned int'
cmd_usbd.c: At top level:
cmd_usbd.c:168: warning: 'run_cmd' defined but not used
cmd_usbd.c: In function 'do_usbd_down':

Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>