net/designware: add error message on DMA reset timeout

If for some reason DMA module fails to reset user oserves only this:
--->---
# dhcp
Trying dwmac.e0018000
FAIL
--->---

This message makes not much sense.
With proposed change error message will be more helpful:
--->---
# dhcp
Trying dwmac.e0018000
DMA reset timeout
FAIL
--->---

For example user may do power toggle to recover board functionality.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Pavel Machek <pavel@denx.de>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Cc: Ian Campbell <ijc@hellion.org.uk>
Cc: Marek Vasut <marex@denx.de>
Reviewed-by: Tom Rini <trini@ti.com>
Acked-by: Pavel Machek <pavel@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/designware.c b/drivers/net/designware.c
index 9ded895..c03e935 100644
--- a/drivers/net/designware.c
+++ b/drivers/net/designware.c
@@ -236,8 +236,10 @@
 
 	start = get_timer(0);
 	while (readl(&dma_p->busmode) & DMAMAC_SRST) {
-		if (get_timer(start) >= CONFIG_MACRESET_TIMEOUT)
+		if (get_timer(start) >= CONFIG_MACRESET_TIMEOUT) {
+			printf("DMA reset timeout\n");
 			return -1;
+		}
 
 		mdelay(100);
 	};