USB: bcma: Add a check for devm_gpiod_get

bcma_hcd_probe misses a check for devm_gpiod_get and may miss
the error.
Add a check for it and return the error if a failure occurs.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Link: https://lore.kernel.org/r/20191016083531.5734-1-hslester96@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>