target/mips: Fix potential integer overflow (CID 1452921)

target/mips: Fix potential integer overflow (CID 1452921)

Use the BIT_ULL() macro to ensure we use 64-bit arithmetic.
This fixes the following Coverity issue (OVERFLOW_BEFORE_WIDEN):

  CID 1452921:  Integer handling issues:

    Potentially overflowing expression "1 << w" with type "int"
    (32 bits, signed) is evaluated using 32-bit arithmetic, and
    then used in a context that expects an expression of type
    "uint64_t" (64 bits, unsigned).

Fixes: 074cfcb4dae ("target/mips: Implement hardware page table walker")
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <20210505215119.1517465[email protected]>