misc: apds990x: Use sysfs_match_string() helper

Use sysfs_match_string() helper instead of open coded variant.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>