pm2301-charger: Reference put missing after access

Added missing pm_runtime_put_sync in read & write.

Signed-off-by: Rupesh Kumar <rupesh.kumar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Sandeep TRIPATHY <sandeep.tripathy@stericsson.com>
Reviewed-by: Philippe LANGLAIS <philippe.langlais@stericsson.com>