i2c: sh_mobile: Mark adapter suspended during suspend

When a driver tries to send an I2C message while the adapter is
suspended, this typically fails with:

    i2c-sh_mobile e60b0000.i2c: Transfer request timed out

Avoid accessing the adapter while it is suspended by marking it
suspended during suspend.  This allows the I2C core to catch this, and
print a warning:

    WARNING: CPU: 1 PID: 13 at drivers/i2c/i2c-core.h:54
__i2c_transfer+0x4a4/0x4e4
    i2c i2c-6: Transfer while suspended

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa@kernel.org>