Unreachable return statement after #endif

[Symanyshyn-IFX]

Several source files contain an early return inside a preprocessor #if/#else block, making the final return statement after #endif unreachable dead code.
IAR Compiler reports this as: Warning[Pe111]: statement is unreachable

The pattern is the same: one preprocessor branch returns early, but a second return sits
after #endif where it can never be reached.

Affected files:

CMSIS-NN/Source/ConvolutionFunctions/arm_convolve_even_s4.c

Line 225 in 22080c6

return ARM_CMSIS_NN_SUCCESS;

CMSIS-NN/Source/ConvolutionFunctions/arm_convolve_get_buffer_sizes_s8.c

Line 129 in 22080c6

return 0;

CMSIS-NN/Source/ConvolutionFunctions/arm_depthwise_conv_fast_s16.c

Line 446 in 22080c6

return ARM_CMSIS_NN_SUCCESS;

CMSIS-NN/Source/ConvolutionFunctions/arm_depthwise_conv_s8_opt.c

Line 421 in 22080c6

return ARM_CMSIS_NN_SUCCESS;

CMSIS-NN/Source/NNSupportFunctions/arm_nn_mat_mult_nt_t_s16.c

Line 355 in 22080c6

return ARM_CMSIS_NN_SUCCESS;

Example (arm_convolve_even_s4.c):

#if defined(ARM_MATH_MVEI)
    // ... main implementation ...
#else
    (void)ctx;
    // ...
    return ARM_CMSIS_NN_NO_IMPL_ERROR;  // early return in #else branch
#endif

    return ARM_CMSIS_NN_SUCCESS;        // unreachable

Suggested fix:

Ensure each preprocessor branch has its own return, and remove the one after #endif:

#if defined(ARM_MATH_MVEI)
    // ... main implementation ...
    return ARM_CMSIS_NN_SUCCESS;
#else
    (void)ctx;
    // ...
    return ARM_CMSIS_NN_NO_IMPL_ERROR;
#endif