cmd: fix return code of 'sf erase'

If the offset or the size passed to the 'sf erase' command exceeds
the size of the SPI flash displaying the command usage is not
helpful. Return CMD_RET_FAILURE instead of CMD_RET_USAGE.

Use the CMD_RET_* constants instead of 0, 1, -1.

Simplify a logical expression in the final return statement.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Dhruva Gole <d-gole@ti.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/cmd/sf.c b/cmd/sf.c
index 20a2e79..11b9c25 100644
--- a/cmd/sf.c
+++ b/cmd/sf.c
@@ -343,27 +343,27 @@
 	ulong size;
 
 	if (argc < 3)
-		return -1;
+		return CMD_RET_USAGE;
 
 	if (mtd_arg_off(argv[1], &dev, &offset, &len, &maxsize,
 			MTD_DEV_TYPE_NOR, flash->size))
-		return -1;
+		return CMD_RET_FAILURE;
 
 	ret = sf_parse_len_arg(argv[2], &size);
 	if (ret != 1)
-		return -1;
+		return CMD_RET_USAGE;
 
 	/* Consistency checking */
 	if (offset + size > flash->size) {
 		printf("ERROR: attempting %s past flash size (%#x)\n",
 		       argv[0], flash->size);
-		return 1;
+		return CMD_RET_FAILURE;
 	}
 
 	if (flash->flash_is_unlocked &&
 	    !flash->flash_is_unlocked(flash, offset, len)) {
 		printf("ERROR: flash area is locked\n");
-		return 1;
+		return CMD_RET_FAILURE;
 	}
 
 	ret = spi_flash_erase(flash, offset, size);
@@ -373,7 +373,7 @@
 	else
 		printf("OK\n");
 
-	return ret == 0 ? 0 : 1;
+	return ret ? CMD_RET_FAILURE : CMD_RET_SUCCESS;
 }
 
 static int do_spi_protect(int argc, char *const argv[])