fbdev: sh_mobile_lcdc: Fix destruction of uninitialized mutex

If sh_mobile_lcdc_probe() fails after the allocation of driver-private
data, but before the initialization of all channels, a warning will be
printed due to the destruction of an uninitialized mutex:

    WARNING: CPU: 0 PID: 1 at kernel/locking/mutex-debug.c:116 mutex_destroy+0x5c/0x7c()
    DEBUG_LOCKS_WARN_ON(mutex_is_locked(lock))
    ...
    Backtrace:
    ...
    [<c00425b4>] (mutex_destroy) from [<c01d5858>] (sh_mobile_lcdc_remove+0x1bc/0x230)
     r4:df6a4800 r3:00000000
    [<c01d569c>] (sh_mobile_lcdc_remove) from [<c01d6620>] (sh_mobile_lcdc_probe+0xd54/0xe28)

Move the initialization of the mutexes from sh_mobile_lcdc_channel_init()
to immediately after the allocation of driver-private data to fix this.

Note that the interrupt number is moved to a new variable "irq", so we
can reuse the existing variable "i" for iterating over the channels.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>