rt2x00: Clean up error handling of PCI queue DMA allocation.

When, for some reason, the rt2x00pci module fails to allocate DMA memory for
the queues, it tries to undo the complete initialization of the PCI device,
including freeing of the irq. This results in the following error in dmesg, as
the irq hadn't been requested yet:

[  78.123456] Trying to free already-free IRQ 17

Fix this by implementing proper error handling code, instead of just using the
full uninitialization function.

Signed-off-by: Gertjan van Wingerde <gwingerde@kpnplanet.nl>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>