mmc: dw_mmc: Fix mask in IDMAC_SET_BUFFER1_SIZE macro

The mask used inside this macro was assuming Buffer_Size1's [BS1's]
width to be 14 bits, it is actually 13 bits.  Modify masks used in
IDMAC_SET_BUFFER1_SIZE such that they use only 13 bits instead of
current 14.

Signed-off-by: Shashidhar Hiremath <shashidharh@vayavyalabs.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>