MLK-21590 epdc: fix potential out of array boundary access

MLK-21590 epdc: fix potential out of array boundary access

The function mxc_epdc_fb_init_hw() could be called more than once when load
the firmware due to some reason. If this case happens, then for following codes,
the array fb_data->fw_str pointed to will be accessed out of bound. It probably
causes kernel crash, or makes fb_data->fw_str get a wrong value, then the driver
may be stuck during the process of loading the firmware.

        if (fb_data->cur_mode) {
                strcat(fb_data->fw_str, "imx/epdc/epdc_");
                strcat(fb_data->fw_str, fb_data->cur_mode->vmode->name);
                strcat(fb_data->fw_str, ".fw");
        }

This patch fixed that by using strcpy instread.

Signed-off-by: Robby Cai <robby.cai@nxp.com>
Reviewed-by: Guoniu.Zhou <guoniu.zhou@nxp.com>