coresight: stm: Wrong condition check in unlink function

Wrong method used in parameter check for "entities", intent to zero
check for all bits in the "entities" array, but only check the pointer
so need replaced by bitmap_empty.

Change-Id: Id4ae42ebae3014741780da4450ff4ecbbeb1f2dc
Signed-off-by: Mulu He <muluhe@codeaurora.org>