MFC r296816:

MFC r296816:

libdtrace: use calloc(3) instead of malloc(3) when it makes sense.

calloc(3) is faster and occasionally safer than malloc(3) + bzero(3).

In one case, pointed out by Mark[1], this also cleans up a calculation.

Reviewed by:	markj [1]

git-svn-id: svn://svn.freebsd.org/base/stable/10@297129 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f