alpha: Replace strncmp with str_has_prefix

In commit b6b27355
("tracing: Use str_has_prefix() instead of using fixed sizes")
the newly introduced str_has_prefix() was used
to replace error-prone strncmp(str, const, len).
Here fix codes with the same pattern.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>