shell: fix i2c commands definitions

I2C scan and recover functions didn't have mandatory parameters
specified, which resulted in not displaying the I2C controllers in
help message. Instead, the command was executed, and argv was
dereferenced outside of the bounds, providing invalid data to
device_get_binding function.
Other functions had defined mandatory parameters without taking their
names into account, they are provided as argv[0].

Signed-off-by: Michał Barnaś <mb@semihalf.com>