strict pin controller returns -EINVAL in case of pin request which
is already claimed by somebody else.
Following is the sequence of calling pin_request() from
pinctrl_bind_pins():-
pinctrl_bind_pins()->pinctrl_select_state()->pinmux_enable_setting()->
pin_request()

But pinctrl_bind_pins() only returns -EPROBE_DEFER which makes device
driver probe successful even if the pin request is rejected by the pin
controller subsystem.

This commit modifies pinctrl_bind_pins() to return error if the pin is
rejected by pin control subsystem.

Signed-off-by: Deepak Das <deepak_das@mentor.com>
[Rewrote to be cleaner]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>