mmc: block: Add error handling in mmc_blk_cmdq_part_switch

mmc_blk_cmdq_part_switch always returned 0 even in case of
failures as errors are not handled in this function.
We need to un-halt cmdq in case it's in halt state when
mmc_switch fails. This change adds error handling code and
returns error in case of any failure.

Change-Id: Icd7ec4b7b53fc56d39dbcea195ae44bf08de17e5
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>