configs: mx6sxsabresd: drop CONFIG_SYS_FSL_USDHC_NUM

With DM_MMC, CONFIG_SYS_FSL_USDHC_NUM is not needed.

Reviewed-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
1 file changed