usb: misc: brcmstb-usb-pinmap: add IRQ check

The driver neglects to check the result of platform_get_irq()'s call and
blithely passes the negative error codes to devm_request_irq() (which takes
*unsigned* IRQ #), causing it to fail with -EINVAL, overriding an original
error code.  Stop calling devm_request_irq() with the invalid IRQ #s.

Fixes: 517c4c44

 ("usb: Add driver to allow any GPIO to be used for 7211 USB signals")
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/806d0b1a-365b-93d9-3fc1-922105ca5e61@omp.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>