MicroBlaze: negated errors in lowlevellock.h

The macros in lowlevellock.h are returning positive errors, but the
users of the macros expect negative. This causes e.g. sem_wait to
sometimes return an error with errno set to -EWOULDBLOCK.

Signed-off-by: Kirk Meyer <kirk.meyer@sencore.com>
Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>