Staging: wlan-ng: memory allocated inside mkimage() is not freed if subsequent calls fails.

This patch frees memory allocated inside mkimage() in case mkimage()
or any other subsequent calls inside prism2_fwapply() from prism2fw.c
file fails. To fix this I introduces goto labels where the free
operation is done in case some operations fails. After the introduction
of goto labels has been done, in order to use the same return path,
"return x" instuctions were replaced with "goto" instuctions.

Signed-off-by: Claudiu Beznea <claudiu.beznea@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>