rtla: Fix Makefile when called from -C tools/

rtla: Fix Makefile when called from -C tools/

Sedat Dilek reported an error on rtla Makefile when running:

    $ make -C tools/ clean
    [...]
    make[2]: Entering directory
    '/home/dileks/src/linux-kernel/git/tools/tracing/rtla'
    [...]
    '/home/dileks/src/linux-kernel/git/Documentation/tools/rtla'
    /bin/sh: 1: test: rtla-make[2]:: unexpected operator    <------ The problem
    rm: cannot remove '/home/dileks/src/linux-kernel/git': Is a directory
    make[2]: *** [Makefile:120: clean] Error 1
    make[2]: Leaving directory

This occurred because the rtla calls kernel's Makefile to get the
version in silence mode, e.g.,

    $ make -sC ../../.. kernelversion
    5.19.0-rc4

But the -s is being ignored when rtla's makefile is called indirectly,
so the output looks like this:

    $ make -C ../../.. kernelversion
    make: Entering directory '/root/linux'
    5.19.0-rc4
    make: Leaving directory '/root/linux'

Using 'grep -v make' avoids this problem, e.g.,

    $ make -C ../../.. kernelversion | grep -v make
    5.19.0-rc4

Thus, add | grep -v make.

Link: https://lkml.kernel.org/r/870c02d4d97a921f02a31fa3b229fc549af61a20.1657747763.git.bristot@kernel.org
Fixes: 8619e32825fd ("rtla: Follow kernel version")
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>