Fix F14Table type conversion warning

Summary: The `|` operation causes the  `int to uint8` conversion warning that be treated as an error on some targets and prevent them use F14Map.

Reviewed By: yfeldblum

Differential Revision: D20654932

fbshipit-source-id: 6c909b7b58f4be263b0e30b1aa3acd82b5b9479d

folly/container/detail/F14Table.h

@@ -403,7 +403,8 @@ struct alignas(kRequiredVectorAlignment) F14Chunk {
             scale < (std::size_t{1} << kCapacityScaleBits),
         "");
     if (kCapacityScaleBits == 4) {
-      control_ = (control_ & ~0xf) | static_cast<uint8_t>(scale);
+      control_ =
+          static_cast<uint8_t>((control_ & ~0xf) | static_cast<uint8_t>(scale));
     } else {
       uint16_t v = static_cast<uint16_t>(scale);
       std::memcpy(&tags_[12], &v, 2);