msm: camera: isp: Fix memdup_user sanity check

memdup_user return ERR_PTR in an error scenarios like invalid source
pointer or unable to allocate destination memory. Checking the return
address against integer zero in error case can fail as memdup_user
returns ERR_PTR(non zero ptr value) instead or NULL

Change-Id: I697fe4de5288223bced800506ed6e02904b5d636
Signed-off-by: Tony Lijo Jose <tjose@codeaurora.org>