staging:rtl8192u: Refactor GET_COMMAND_PACKET_FRAG_THRESHOLD - Style

The MACRO GET_COMMAND_PACKET_FRAG_THRESHOLD causes a number of
checkpatch issues so has been refactored to use braces around the
parameter 'v' to avoid precedence issues, and to add spaces around
operators.

These changes are coding style changes which should have no impact
on runtime code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>