spi: s3c64xx: use unsigned type for fifo handling variables

spi: s3c64xx: use unsigned type for fifo handling variables

The 'quirks' variable cannot ever be negative, therefore use u8
instead of int. The 8 bit size is given from the fact that
currently the quirks variable has very few statuses.

The rx_lvl_offset and tx_st_done store shift values, so that u8
is a proper size.

fifo_lvl_mask stores a series of masks, to be in we will keep the
32 bit size.

Change-Id: I949160c9dfd68d6dce5c2385c911269f5b6d1505
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Andi Shyti <andi.shyti@samsung.com>