ARM: OMAP2+: Fix device node reference counts

ARM: OMAP2+: Fix device node reference counts

After commit 0549bde0fcb1 ("of: fix of_node leak caused in
of_find_node_opts_by_path"), the following error may be
reported when running omap images.

OF: ERROR: Bad of_node_put() on /ocp@68000000
CPU: 0 PID: 0 Comm: swapper Not tainted 4.10.0-rc7-next-20170210 #1
Hardware name: Generic OMAP3-GP (Flattened Device Tree)
[<c0310604>] (unwind_backtrace) from [<c030bbf4>] (show_stack+0x10/0x14)
[<c030bbf4>] (show_stack) from [<c05add8c>] (dump_stack+0x98/0xac)
[<c05add8c>] (dump_stack) from [<c05af1b0>] (kobject_release+0x48/0x7c)
[<c05af1b0>] (kobject_release)
	from [<c0ad1aa4>] (of_find_node_by_name+0x74/0x94)
[<c0ad1aa4>] (of_find_node_by_name)
	from [<c1215bd4>] (omap3xxx_hwmod_is_hs_ip_block_usable+0x24/0x2c)
[<c1215bd4>] (omap3xxx_hwmod_is_hs_ip_block_usable) from
[<c1215d5c>] (omap3xxx_hwmod_init+0x180/0x274)
[<c1215d5c>] (omap3xxx_hwmod_init)
	from [<c120faa8>] (omap3_init_early+0xa0/0x11c)
[<c120faa8>] (omap3_init_early)
	from [<c120fb2c>] (omap3430_init_early+0x8/0x30)
[<c120fb2c>] (omap3430_init_early)
	from [<c1204710>] (setup_arch+0xc04/0xc34)
[<c1204710>] (setup_arch) from [<c1200948>] (start_kernel+0x68/0x38c)
[<c1200948>] (start_kernel) from [<8020807c>] (0x8020807c)

of_find_node_by_name() drops the reference to the passed device node.
The commit referenced above exposes this problem.

To fix the problem, use of_get_child_by_name() instead of
of_find_node_by_name(); of_get_child_by_name() does not drop
the reference count of passed device nodes. While semantically
different, we only look for immediate children of the passed
device node, so of_get_child_by_name() is a more appropriate
function to use anyway.

Release the reference to the device node obtained with
of_get_child_by_name() after it is no longer needed to avoid
another device node leak.

While at it, clean up the code and change the return type of
omap3xxx_hwmod_is_hs_ip_block_usable() to bool to match its use
and the return type of of_device_is_available().

Cc: Qi Hou <qi.hou@windriver.com>
Cc: Peter Rosin <peda@axentia.se>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>