msm: camera: isp: Preserve the default min hbi value.

For the IPP & PPP paths the default min hbi between lines
is specified to be 4. The value is overwritten while
configuring other bits in this register. This change ensures
that we retain the default register value for min hbi.

Signed-off-by: Karthik Anantha Ram <kartanan@codeaurora.org>
Change-Id: If39c58f7208d61e711d32000f5481d99f6fc80c5