Additional fix for -DNO_CLEAN build across r353340 and r353381

opensolaris_atomic.S is now only used on i386 with opensolaris_atomic.c
used on other platforms. After r353381 it doesn't exist on those
platforms so the stale dependency would result in a build error.

r353408 addressed this issue for cddl/lib/libzpool, but it persisted
with the opensolaris and zfs modules.