ARM: davinci: dm646x-evm: Simplify error handling in 'evm_sw_setup()'

There is no need to call 'gpio_free(evm_sw_gpio[i])' for these error
handling cases, it is already done in the error handling path at label
'out_free'.

Simplify the code and axe a few LoC.

While at it, also explicitly return 0 in the normal path.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>