rtc-pcf8583: Check for i2c adapter functionality

Not all i2c adapters support I2C-level messaging.  Check that the adapter
does before probing for a PCF8583 chip, as the driver makes use of
i2c_transfer and i2c_master_send.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>