V4L/DVB (7715): pvrusb2: Clean out all use of __FUNCTION__

Apparently the kernel developers no longer consider it proper
etiquette to use __FUNCTION__; everyone must instead use __func__
(even though it breaks with older compilers).  And worse still, actual
effort is being expended to sweep this change throughout the kernel
source tree.  Don't these people have better things to do?  So...
Completely clean out all use of __FUNCTION__ from the pvrusb2 driver
(it was just in the sysfs interface).  I'm not going to use __func__
either.  So there.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>