dsp: add an exception in determining port type

AFE ports have been identified as RX or TX based
on a certain rule. Add an exception for VOICE_RECORD_TX
port from this rule.

Change-Id: I8a2fa4b6053baaf7747493aa385da887e6dd170c
Signed-off-by: Vikram Panduranga <vpandura@codeaurora.org>