Refactor MLA decode kernel: Replace T.If with native Python if statement (#162)

Simplify the control flow in the MLA decode kernel by replacing TileLang's T.If construct with a standard Python if statement. This change improves code readability and maintains the existing logic for handling sequence length constraints during block-wise computation.

Author: LeiWang1999

examples/deepseek_mla/example_mla_decode_paged.py

@@ -73,7 +73,7 @@ def flash_mla_kernel(
                     policy=T.GemmWarpPolicy.FullCol)
                 T.copy(scores_max, scores_max_prev)
                 T.fill(scores_max, -T.infinity(accum_dtype))
-                with T.If(kr == 0), T.Then():
+                if kr == 0:
                     for i, j in T.Parallel(block_H, block_N):
                         acc_s[i, j] = T.if_then_else(k * block_N + j >= CACHE_SEQLENS[bx], -T.infinity(accum_dtype), acc_s[i, j])
                 T.reduce_max(acc_s, scores_max, dim=1, clear=False)