msm: camera: ispif: Use proper type while comparing negative values.

Not using the proper type to compare against negative values
will not work in case of 64bit build because long and int types
have different ranges for LP64 builds. So fix it by using a proper
cast.

Change-Id: I80c7701f3d41ceb27cae7293df5c6ca5578c34cd
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>