MAINTAINERS: adjust kprobes.rst entry to new location

Commit 2165b82f ("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.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

MAINTAINERS

@@ -9597,7 +9597,7 @@ M:	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
 M:	"David S. Miller" <davem@davemloft.net>
 M:	Masami Hiramatsu <mhiramat@kernel.org>
 S:	Maintained
-F:	Documentation/staging/kprobes.rst
+F:	Documentation/trace/kprobes.rst
 F:	include/asm-generic/kprobes.h
 F:	include/linux/kprobes.h
 F:	kernel/kprobes.c