msm: kgsl: Update addr variable in kgsl_get_unmapped_area

If the addr variable exceeds KGSL_SVM_UPPER_BOUND we take care of
the high limit to the vm_unmapped_area() call but never actually
update the addr variable. Therefore, if we have an addr exceeding
our mmap range and vm_unmapped_area returns failure, then we simply
use the invalid addr value for the mmap_range_valid() check which
fails.

Fix this by updating the addr with the returned value of the
unmapped area. Also fix the low limits from TASK_UNMAPPED_BASE to
SZ_1M since the former value is very large for 64 bit.

Change-Id: I33cf736e07cdf095b1552407f71dd79e435393f0
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>