Adapt quad lib to RIOT coding conventions

sys/quad_math/adddi3.c

sys/quad_math/anddi3.c

sys/quad_math/ashldi3.c

sys/quad_math/ashrdi3.c

sys/quad_math/cmpdi2.c

sys/quad_math/divdi3.c

sys/quad_math/fixdfdi.c

sys/quad_math/fixsfdi.c

sys/quad_math/fixunsdfdi.c

sys/quad_math/fixunssfdi.c

sys/quad_math/floatdidf.c

sys/quad_math/floatdisf.c

sys/quad_math/floatunsdidf.c

sys/quad_math/iordi3.c

sys/quad_math/lshldi3.c

sys/quad_math/lshrdi3.c

sys/quad_math/moddi3.c

sys/quad_math/muldi3.c

sys/quad_math/negdi2.c

sys/quad_math/notdi2.c