fbdev: sh_mobile_lcdcfb: fix module lock acquisition

Whenever the LCDC is to be started or stopped, a board callback is
checked for existence and invoked. Prior to the invokation, the
callback's module lock is also acquired, to be released once the
callback returns. However, the order of testing makes it possible for
the lock to be acquired and not released in case the callback does not
exist. This patch reorders the tests to prevent this particular case.

Signed-off-by: Alexandre Courbot <gnurou@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>