cmd: mmc: check whether card is SD or eMMC before hwpartition

It doesn't need to follow more sequence to do the hwparititioning,
because SD doesn't support hwpartitioning feature.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>