mmc: mmci: Change struct members from bool to u8

Recent versions of checkpatch have a new warning based on a documented
preference of Linus to not use bool in structures due to wasted space and
the size of bool is implementation dependent.  For more information, see
the email thread at https://lkml.org/lkml/2017/11/21/384

fix checkpatch --strict issues:
-CHECK: Avoid using bool structure members because of possible alignment
 issues - see: https://lkml.org/lkml/2017/11/21/384


-WARNING: Avoid using bool as bitfield. Prefer bool bitfields as
 unsigned int or u<8|16|32>

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>