msm: vidc: venc: Layer bitrate setting bug fix

In ext controls we cannot have multiple controls with same
ID. If we have multiple controls with same ID, then the
value of these controls is overwritten with last value.
To prevent this happening for layered bitrate we now only
set bitrate for only layer per s_ext_ctrl call.

CRs-Fixed: 2012385
Change-Id: I58914e5026bb40c0a37f502d34302a65935a2b2d
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>