mx6sabresd: Reset counter to prevent error message

If a HDMI cable is not connected, the following message is seen on boot:

CPU:   Freescale i.MX6Q rev1.1 at 792 MHz
Reset cause: POR
Board: MX6-SabreSD
DRAM:  1 GiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
No panel detected: default to HDMI
unsupported panel HDMI

Reset the 'i' variable to fix the 'unsupported panel' message.

This follows the same idea of commit 47ac53d7 (imx: nitrogen6x/mx6qsabrelite:
Fix bug in board_video_skip).
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>

board/freescale/mx6sabresd/mx6sabresd.c

@@ -322,6 +322,7 @@ int board_video_skip(void)
 		if (!panel) {
 			panel = displays[0].mode.name;
 			printf("No panel detected: default to %s\n", panel);
+			i = 0;
 		}
 	} else {
 		for (i = 0; i < ARRAY_SIZE(displays); i++) {