staging: lustre: discard LOWEST_BIT_SET()

This macro is only used once to test if a value is
a power of two.  So use is_power_of_2() instead and
discard the macro.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>