[POWERPC] Remove dev_dbg redefinition in drivers/ps3/vuart.c

Commit 404d5b18 changed the definition
of dev_dbg in the !DEBUG case from being a #define to being a static
inline.  There was code in drivers/ps3/vuart.c to do exactly that,
which fails to compile now.  This fixes it by removing the redefinition,
as the redefinition is now superfluous.

Signed-off-by: Paul Mackerras <paulus@samba.org>