ASoC: Change to correctly set the BTSCO Sample Rate

 This mixer control would always set the default value of
 BT SCO Sample ate as there is no matching case.
 The change ensures appropriate enum texts are used instead
 and the cases are appropriately modified to ensure a match.

Change-Id: I097b20a4983e7c4eae29e97803e36fcfc14fb8b2
Signed-off-by: Shreyas Nagasandra Chandrasekhar <snagas@codeaurora.org>