qpnp-pin: Fix null pointer access in qpnp_pin_debugfs_create()

qpnp_pin_debugfs_create() is going through all the child nodes
to create debugfs entries whereas the allocation for q_spec is
made only for available child nodes. This leads to a null pointer
access when CONFIG_GPIO_QPNP_PIN_DEBUG is selected in defconfig.
Fix it by using number of gpios available under each gpio chip
which was populated from the available child count already.

Change-Id: I17cbeeba158d34180763087103da4b03e01f7c90
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>