Staging: kpc2000: kpc_dma: Make some symbols static

Fix sparse warnings:

drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c:46:6: warning: symbol 'kpc_dma_del_device' was not declared. Should it be static?
drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c:84:1: warning: symbol 'dev_attr_engine_regs' was not declared. Should it be static?
drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c:91:14: warning: symbol 'kpc_dma_class' was not declared. Should it be static?
drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c:199:24: warning: symbol 'kpc_dma_plat_driver_i' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>