media: cx23888: remove unused functions

Found with clang:
drivers/media/pci/cx23885/cx23888-ir.c:178:19: warning: unused function 'ns_to_clock_divider' [-Wunused-function]
static inline u16 ns_to_clock_divider(unsigned int ns)
                  ^
drivers/media/pci/cx23885/cx23888-ir.c:184:28: warning: unused function 'clock_divider_to_ns' [-Wunused-function]
static inline unsigned int clock_divider_to_ns(unsigned int divider)
                           ^
drivers/media/pci/cx23885/cx23888-ir.c:202:19: warning: unused function 'freq_to_clock_divider' [-Wunused-function]
static inline u16 freq_to_clock_divider(unsigned int freq,
                  ^

Cc: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>