samples: posix: uname: Set to 1cpu as shell_thread is not SMP-safe

The sample will leverage shell_thread function, which is not SMP-safe.
This will cause issues on some SMP platform. Set CONFIG_MP_MAX_NUM_CPUS
to 1 to fix the issue.

Signed-off-by: Jaxson Han <[email protected]>

Author: povergoing

samples/posix/uname/prj.conf

@@ -1,3 +1,4 @@
 CONFIG_POSIX_API=y
 CONFIG_SHELL=y
 CONFIG_SHELL_GETOPT=y
+CONFIG_MP_MAX_NUM_CPUS=1