mmc: block: Don't unhalt if switch to CQ mode fails

There's no reason to unhalt if switching to CQ mode fails.
Since card is not in CQ mode, let the controller be halted.
The caller will handle this error.

CRs-fixed: 2241401
Change-Id: I307753ad66d291168a55f760565cc141d7c83c31
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>