selftests/proc: fix string literal warning in proc-maps-race.c

selftests/proc: fix string literal warning in proc-maps-race.c

This change resolves non literal string format warning invoked for
proc-maps-race.c while compiling.

proc-maps-race.c:205:17: warning: format not a string literal and no format arguments [-Wformat-security]
 205 |                 printf(text);
     |                 ^~~~~~
proc-maps-race.c:209:17: warning: format not a string literal and no format arguments [-Wformat-security]
 209 |                 printf(text);
     |                 ^~~~~~
proc-maps-race.c: In function `print_last_lines':
proc-maps-race.c:224:9: warning: format not a string literal and no format arguments [-Wformat-security]
 224 |         printf(start);
     |         ^~~~~~

Add string format specifier %s for the printf calls in both
print_first_lines() and print_last_lines() thus resolving the warnings.

The test executes fine after this change thus causing no effect to the
functional behavior of the test.

Link: https://lkml.kernel.org/r/20250804225633.841777-1-hsukrut3@gmail.com
Fixes: aadc099c480f ("selftests/proc: add verbose mode for /proc/pid/maps tearing tests")
Signed-off-by: Sukrut Heroorkar <hsukrut3@gmail.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Cc: David Hunter <david.hunter.linux@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>