Revert "tty: serial: add missing spin_lock_init for SiFive serial console"

This reverts commit 17b4efdf.

There has been a quick fix against uninitialised lock revealed by
the commit f743061a ("serial: core: Initialise spin lock before use
in uart_configure_port()"). Since we have now better fix in serial core,
this may be safely reverted.

Fixes: 17b4efdf ("tty: serial: add missing spin_lock_init for SiFive serial console")
Depends-on: f743061a

 ("serial: core: Initialise spin lock before use in uart_configure_port()")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200711135346.71171-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>