Refactor get_n_parts function to simplify code and improve readability

convert-pth-to-ggml.py

@@ -37,17 +37,16 @@ fname_hparams   = sys.argv[1] + "/params.json"
 fname_tokenizer = sys.argv[1] + "/../tokenizer.model"
 
 def get_n_parts(dim):
-    if dim == 4096:
-        return 1
-    elif dim == 5120:
-        return 2
-    elif dim == 6656:
-        return 4
-    elif dim == 8192:
-        return 8
-    else:
-        print("Invalid dim: " + str(dim))
+    mappings = {
+        4096: 1,
+        5120: 2,
+        6656: 4,
+        8192: 8
+    }
+    if dim not in mappings:
+        print(f"Invalid dim: {dim}")
         sys.exit(1)
+    return mappings[dim]
 
 # possible data types
 #   ftype == 0 -> float32