spi/i.MX: fix broken error handling for gpio_request

spi/i.MX: fix broken error handling for gpio_request

i.MX35-provided chipselects are represented using negative numbers. If
gpio_request() fails and the previous chipselect was a negative number,
the while loop is endless (i is never decremented).

Also, the error loop would never call gpio_free on chipselect[0].

And finally, the error message was missing an endline.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>