isl29003: fix resume functionality

The isl29003 does not interpret the return value of
i2c_smbus_write_byte_data() correctly and hence causes an error on system
resume.

Also introduce power_state_before_suspend and restore the chip's power
state upon wakeup.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>