string: use __attribute__((nonnull())) in strends()

The arguments of strends() must not be NULL so annotate the function
with the nonnull attribute.

Suggested-by: Kees Cook <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

include/linux/string.h

···
  * Returns:
  * True if @str ends with @suffix. False in all other cases.
  */
-static inline bool strends(const char *str, const char *suffix)
+static inline bool __attribute__((nonnull(1, 2)))
+strends(const char *str, const char *suffix)
 {
 	unsigned int str_len = strlen(str), suffix_len = strlen(suffix);