msm: camera: isp: Get the first active req during bubble

Sometimes, UMD reports nonincrementing shutter request id
issue during monkey test on sHDR usecase, isp reports last
one req in active req list during bubble, so if the active
req count is 2, we will meet this issue.
This change gets the first active req during bubble in case
the active req cnt is 2.

CRs-Fixed: 2885087
Change-Id: I67d1ecfe9c88123e6d0887383961bfc676455a0d
Signed-off-by: Depeng Shao <depengs@codeaurora.org>