USB: gadget: f_mass_storage: put_device() in error recovery

This commit fixes an issue with error recovery after
device_register() fails in Mass Storage Function.  The device
needs to be put to avoid resource leakage.

Signed-off-by: Rahul Ruikar <rahul.ruikar@gmail.com>
[mina86@mina86.com: updated commit message]
Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>