pm2301_charger: Fix NULL pointer dereference

Add checking pl_data in probe, this prevent possible NULL pointer
dereference. Also fix NULL pointer deference in dev_err when allocate
memory for pm2 fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>