staging: comedi: serial2002: remove pr_err() noise in serial2002_read()

This pr_err() is just added noise, the user can't do anything about it.
Just remove it.

Since this is the only pr_level() message in the driver, also remove
the pr_fmt() macro.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>