Fix oti6858 debug level

For some reason the oti6858 driver undefines and redefines the dbg
macro. This makes it spew debugging messages at KERN_INFO instead of
KERN_DEBUG.

This patch removes the undef and define making the driver log like every
other USB serial driver.

Signed-off-by: Scott Ashcroft <scott.ashcroft@talk21.com>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>