dmaengine: edma: Rename set_bits and remove unused clear_bits helper

The clear_bits() helper is not used by the driver so it can be removed.

powerpc architecture defines the set_bits() in
arch/powerpc/include/asm/bitops.h which results failed compile testing on
powerpc architecture:

>> drivers/dma/edma.c:415:20: error: conflicting types for 'set_bits'
    static inline void set_bits(int offset, int len, unsigned long *p)
                       ^~~~~~~~
   In file included from include/linux/bitops.h:36:0,
                    from include/linux/kernel.h:10,
                    from include/linux/list.h:8,
                    from include/linux/kobject.h:20,
                    from include/linux/device.h:17,
                    from include/linux/dmaengine.h:20,
                    from drivers/dma/edma.c:16:
   arch/powerpc/include/asm/bitops.h:75:14: note: previous definition of 'set_bits' was here
    DEFINE_BITOP(set_bits, or, "")
                 ^
   arch/powerpc/include/asm/bitops.h:58:24: note: in definition of macro 'DEFINE_BITOP'
    static __inline__ void fn(unsigned long mask, \
                           ^~

>> drivers/dma/edma.c:421:20: error: conflicting types for 'clear_bits'
    static inline void clear_bits(int offset, int len, unsigned long *p)
                       ^~~~~~~~~~
   In file included from include/linux/bitops.h:36:0,
                    from include/linux/kernel.h:10,
                    from include/linux/list.h:8,
                    from include/linux/kobject.h:20,
                    from include/linux/device.h:17,
                    from include/linux/dmaengine.h:20,
                    from drivers/dma/edma.c:16:
   arch/powerpc/include/asm/bitops.h:76:14: note: previous definition of 'clear_bits' was here
    DEFINE_BITOP(clear_bits, andc, "")
                 ^
   arch/powerpc/include/asm/bitops.h:58:24: note: in definition of macro 'DEFINE_BITOP'
    static __inline__ void fn(unsigned long mask, \
                           ^~

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>