power: smb135x-charger: retry i2c read/writes

The SMB chip could fail i2c transactions. Retry few times with
increasing sleep times between them.

Change-Id: I78a75d4bd9c1392f23da4e2715161bfd7128db28
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>