msm: kgsl: Fix use of uninitialized memory

Use kzalloc() to avoid uninitialized buffer reading
in profile_assignments_read(). This will fix use of
uninitialized memory in case if it is not enter into
loop to fill the buffer in profile_assignments_read().

Change-Id: Ib0b78564c2ec4298e6938ec76d031106469e16ef
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>