mmc:prevent accessing to the released space in case of wrong usage

1.Since in mmc_init, the most of mmc_device_info passed in are temporary variables.
  In order to avoid referencing the released space on the stack when maybe MISUSED,
  it`s better to use global variables to store mmc_device_info in mmc.c
2.Delete redundant;

Signed-off-by: deqi.hu@siengine.com
Change-Id: I51ae90e7f878b19b4963508b3f7ec66339015ebc
1 file changed