mmc: core: Fix placement of crash_on_err in mmc_host's struct

The crash_on_err member of the mmc_host structure is incorrectly
placed in the mmc_host's private data area. This error could cause data
corruption and unintended behavior.

Change-Id: I396226800d186093c9cb41f74309f4a46f781c45
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>