intel: fix un-blanced map_refcount issue

intel: fix un-blanced map_refcount issue

This is a regression introduced by commit cdcfd5, which forget to
increase the map_refcount for successfully-mapped region. Thus caused a
wrong non-blanced map_refcount.

This would fix the regression found in the two following webglc testcase
on Pineview platform:
   texture-npot.html
   gl-max-texture-dimensions.html

Cc: Anuj Phogat <anuj.phogat@gmail.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>