rtla: Fix systme -> system typo on man page

Link: https://lkml.kernel.org/r/YhZsZxqk+IaFxorj@kernel.org

Fixes: 496082df ("rtla: Add rtla osnoise man page")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Documentation/tools/rtla/common_osnoise_description.rst

 The **rtla osnoise** tool is an interface for the *osnoise* tracer. The
 *osnoise* tracer dispatches a kernel thread per-cpu. These threads read the
 time in a loop while with preemption, softirq and IRQs enabled, thus
-allowing all the sources of operating systme noise during its execution.
+allowing all the sources of operating system noise during its execution.
 The *osnoise*'s tracer threads take note of the delta between each time
 read, along with an interference counter of all sources of interference.
 At the end of each period, the *osnoise* tracer displays a summary of