net: qrtr: Handle error from skb_put_padto

skb_put_padto() will free the skb if it fails to add the requested
padding to the skb. Drop the packet if we are unable to allocate a new
skb with the requested padding.

Change-Id: I5503c99679c7e6ecf767d3f632d72da5315988f1
Signed-off-by: Chris Lew <clew@codeaurora.org>