Fix the problem of x_source and y_source causing radial error

Fix the problem of x_source and y_source causing radial error

 The x_source and y_source cause some problem in
 gradient. The old way to handle it by recaulate P1 P2
 to minus the x_source and y_source, but this causes
 problem in radial shader. Now we modify the manner to
 set the texture coordinates: (x_source, y_source) -->
 (x_source + width, y_source + height) to handle all the
 cases.

Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Signed-off-by: Junyan He <junyan.he@linux.intel.com>
Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>