Correct SPL uses of CMD_TFTPPUT

This converts 3 usages of this option to the non-SPL form, since there is
no SPL_CMD_TFTPPUT defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/net.c b/cmd/net.c
index 4227321..d5e2084 100644
--- a/cmd/net.c
+++ b/cmd/net.c
@@ -280,7 +280,7 @@
 
 	switch (argc) {
 	case 1:
-		if (CONFIG_IS_ENABLED(CMD_TFTPPUT) && proto == TFTPPUT)
+		if (IS_ENABLED(CONFIG_CMD_TFTPPUT) && proto == TFTPPUT)
 			return 1;
 
 		/* refresh bootfile name from env */
@@ -289,7 +289,7 @@
 		break;
 
 	case 2:
-		if (CONFIG_IS_ENABLED(CMD_TFTPPUT) && proto == TFTPPUT)
+		if (IS_ENABLED(CONFIG_CMD_TFTPPUT) && proto == TFTPPUT)
 			return 1;
 		/*
 		 * Only one arg - accept two forms:
@@ -311,7 +311,7 @@
 		break;
 
 	case 3:
-		if (CONFIG_IS_ENABLED(CMD_TFTPPUT) && proto == TFTPPUT) {
+		if (IS_ENABLED(CONFIG_CMD_TFTPPUT) && proto == TFTPPUT) {
 			if (parse_addr_size(argv))
 				return 1;
 		} else {