pinctrl: msm: Add error checking for node before accessing it

Every pintype supported may not be added in the device tree.
This can cause certain pintype nodes to be null. Check for this
before accessing the node.

Change-Id: I22891b0e022fa10d11b70f9d8d04b46d660e08c0
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>