staging: rtl8712: Remove while loop and check_cmd_fifo()

Remove while loop as it only runs while the function check_cmd_fifo
returns _FAIL, whereas check_cmd_fifo always returns _SUCCESS (and hence
this loop will never run).
Remove now unused function check_cmd_fifo.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Link: https://lore.kernel.org/r/20190808064012.12661-9-nishkadg.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>