mmc: host: Add check for post tuning in HS400

'commit 34e4cf13f729 ("mmc: core: Update HS400 timing
mode before performing tuning")' updates timing mode
to HS400 before tuning in mmc_hs200_tuning.
On 4.4 kernel, there is check added to bail out from
execute_tuning if HS400 tuning is done in HS200 mode.

Adding check to avoid bailing out and allow
execute_tuning if POST_TUNING capability is set.

Change-Id: I259da28050e5da0c96251cb99176386927b596f0
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>