input: touchscreen: Correct return value check in Goodix driver

Correct return value check of gtp_read_fw_version, called in probe
of the Goodix driver. The return value is actually the number of
registers read through gtp_i2c_read() function call.
Also change the error message of gtp_check_product_id.

Change-Id: I0b643e250a487f08a19555237802b020b0873d1a
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>