goldfish: Use dedicated macros instead of manual bit shifting

There are dedicated macros (lower_32_bits and upper_32_bits)
available to extract the lower and upper 32 bits. They provide
better readability and could prevent some compilation warnings.

Signed-off-by: Roman Kiryanov <rkir@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>