sbrk: Superfluous public function mbed_krbs_ex

[LiyouZhou]

https://github.com/ARMmbed/core-util/blob/master/source/sbrk.cpp#L59

void * mbed_krbs_ex(const ptrdiff_t size, ptrdiff_t *actual)

Is used in:

void * mbed_krbs(const ptrdiff_t size)
{
    return mbed_krbs_ex(size, NULL);
}

Few issues:

1. It is unclear why is mbed_krbs_ex public, and what is the purpose of the actual parameter.
2. https://github.com/ARMmbed/core-util/blob/master/source/sbrk.cpp#L82 this line does not seem to do anything.

@bogdanm Can you comment on this?

[LiyouZhou]

@0xc0170 for watching this issue.

[ciarmcom]

ARM Internal Ref: IOTSFW-2099