ARM: dts: msm: Add MAD specific DMIC clk rate for msm8994

The Digital MIC (DMIC) clock rate that is used by MAD (Microphone
Activity Detection) block on the codec is configurable depending on the
type of on-board DMIC. Add MAD specific DMIC clock rate for msm8994.

CRs-fixed: 692015
Change-Id: I9b571cdaf87da24bae7db031fb0beb6ba77df0db
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>