staging: vt6656: Return error code in vnt_rf_write_embedded function

Use the error code returned by the vnt_control_out function as the
returned value of the vnt_rf_write_embedded function instead of a
boolean value.

Then, fix all vnt_rf_write_embedded calls removing the "and" operations
and replace with a direct assignment to the ret variable and add a check
condition after every call.

Also replace the boolean values true or false in the vnt_rf_set_txpower
function to 0 or error code EINVAL to follow the coding style guide.

The vnt_rf_set_txpower function is called only in the vnt_rf_setpower
function that already returns error codes. The calls to this function
(vnt_rf_set_txpower) not use the returned values, so they not need to be
fixed.

Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Link: https://lore.kernel.org/r/20200414153849.5785-2-oscar.carter@gmx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>