Merge pull request #26061 from penghuiho:fix-pow-bug

Fixed the simd bugs of iPow8u and iPow16u #26061

Add the following cases in opencv_perf_core:

* OCL_PowFixture_iPow.iPow/0, where GetParam() = (640x480, 8UC1)
* OCL_PowFixture_iPow.iPow/2, where GetParam() = (640x480, 16UC1)

iPow8u and iPow16u failed to call to simd accelerating while executing.

Fix the bug by changing the input type of iPow_SIMD function.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [ ] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/core/src/mathfuncs.cpp

@@ -791,7 +791,7 @@ struct iPow_SIMD
 #if (CV_SIMD || CV_SIMD_SCALABLE)
 
 template <>
-struct iPow_SIMD<uchar, int>
+struct iPow_SIMD<uchar, unsigned>
 {
     int operator() ( const uchar * src, uchar * dst, int len, int power )
     {
@@ -871,7 +871,7 @@ struct iPow_SIMD<schar, int>
 };
 
 template <>
-struct iPow_SIMD<ushort, int>
+struct iPow_SIMD<ushort, unsigned>
 {
     int operator() ( const ushort * src, ushort * dst, int len, int power)
     {