mmc: dw_mmc: Fix coding style issues

This patch fixes the following issues reported by checkpatch.pl:
- use -EINVAL instead of -ENOSYS, to fix warning message:
   "ENOSYS means 'invalid syscall nr' and nothing else"
- split lines whose length is greater than 80 characters
- avoid quoted string split across lines
- use min_t instead of min, to fix warning message:
   "min() should probably be min_t(int, cnt, host->part_buf_count)"
- fix missing a blank line after declarations

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>