linux-nilrt-next.inc: B -> STAGING_KERNEL_BUILDDIR
linux-nilrt-next.inc: B -> STAGING_KERNEL_BUILDDIR

Minor change to make the intent clear. Functionally
the same.

Signed-off-by: Chaitanya Vadrevu <3811a3cb328197c46ad44d4be31bbd66ea52bfbb@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt