bus: bt1-apb: Use sysfs_streq instead of strncmp

bus: bt1-apb: Use sysfs_streq instead of strncmp

There is a ready-to-use method to compare a retrieved from a sysfs node
string with another string. It treats both NUL and newline-then-NUL as
equivalent string terminations. So use it instead of manually truncating
the line length in the strncmp() method.

Link: https://lore.kernel.org/r/20200528145050.5203-4-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Olof Johansson <olof@lixom.net>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: soc@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>