common: mmc: unsigned char compared against 0

"enable" is unsigned char type and its value will not be
negative, so discard "enable < 0".

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Diego Santa Cruz <Diego.SantaCruz@spinetix.com>
Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/cmd_mmc.c

@@ -747,7 +747,7 @@ static int do_mmc_rst_func(cmd_tbl_t *cmdtp, int flag,
 	dev = simple_strtoul(argv[1], NULL, 10);
 	enable = simple_strtoul(argv[2], NULL, 10);
 
-	if (enable > 2 || enable < 0) {
+	if (enable > 2) {
 		puts("Invalid RST_n_ENABLE value\n");
 		return CMD_RET_USAGE;
 	}