rtla/timerlat: Simplify RTLA_NO_BPF environment variable check

The code that checks the RTLA_NO_BPF environment variable calls
getenv() twice and uses strncmp() with a length of 2 to compare
against the single-character string "1". This is inefficient and
the comparison length is unnecessarily long.

Store the result of getenv() in a local variable to avoid the
redundant call, and replace strncmp() with strncmp_static() for
the exact match comparison. This follows the same pattern
established in recent commits that improved string comparison
consistency throughout the rtla codebase.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260309195040.1019085-15-wander@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Author: walac

tools/tracing/rtla/src/timerlat.c

@@ -28,12 +28,13 @@ int
 timerlat_apply_config(struct osnoise_tool *tool, struct timerlat_params *params)
 {
 	int retval;
+	const char *const rtla_no_bpf = getenv("RTLA_NO_BPF");
 
 	/*
 	 * Try to enable BPF, unless disabled explicitly.
 	 * If BPF enablement fails, fall back to tracefs mode.
 	 */
-	if (getenv("RTLA_NO_BPF") && strncmp(getenv("RTLA_NO_BPF"), "1", 2) == 0) {
+	if (rtla_no_bpf && strncmp_static(rtla_no_bpf, "1") == 0) {
 		debug_msg("RTLA_NO_BPF set, disabling BPF\n");
 		params->mode = TRACING_MODE_TRACEFS;
 	} else if (!tep_find_event_by_name(tool->trace.tep, "osnoise", "timerlat_sample")) {