MAINTAINERS: adjust kprobes.rst entry to new location

MAINTAINERS: adjust kprobes.rst entry to new location

Commit 2165b82fde82 ("docs: Move kprobes.rst from staging/ to trace/")
moved kprobes.rst, but missed to adjust the MAINTAINERS entry.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches    F:    Documentation/staging/kprobes.rst

Adjust the entry to the new file location.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Link: https://lore.kernel.org/r/20200726055843.10783-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>