cmd: fpga: Move error handling to do_fpga()

Clean fpga_get_op() error handling by moving checking/print to do_fpga.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/fpga.c b/cmd/fpga.c
index 791fe5c..abe6837 100644
--- a/cmd/fpga.c
+++ b/cmd/fpga.c
@@ -74,6 +74,9 @@
 	op = (int)fpga_get_op(argv[1]);
 
 	switch (op) {
+	case FPGA_NONE:
+		printf("Unknown fpga operation \"%s\"\n", argv[1]);
+		return CMD_RET_USAGE;
 #if defined(CONFIG_CMD_FPGA_LOADFS)
 	case FPGA_LOADFS:
 		if (argc < 9)
@@ -360,9 +363,6 @@
 		op = FPGA_LOADS;
 #endif
 
-	if (op == FPGA_NONE)
-		printf("Unknown fpga operation \"%s\"\n", opstr);
-
 	return op;
 }