i2c: sun6i-p2wi: Fix an error message in probe()

The "ret" variable is uninitialized.  It was the "p2wi->rstc" variable
that was intended.  We can also use the %pe string format to print the
error code name instead of just the number.

Fixes: 75ff8a34 ("i2c: sun6i-p2wi: Use devm_clk_get_enabled()")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>