mmc: arm_pl180: Limit data transfer to U16_MAX

mmc: arm_pl180: Limit data transfer to U16_MAX

Currently fetching files bigger that cause a data transfer greater than
U16_MAX fails.

The reason is that the specification defines the datalength register
as a 16 bit wide register, but in u-boot it is used as if it is an
32 bit register. Therefore values greater than U16_MAX cause an
infinite loop inside u-boot. U-boot expects to get more data from
interface/hardware then it will ever get and therefore inifintely waits
for more data that will never come.

Signed-off-by: Maximilian Brune <[email protected]>
Cc: Peng Fan <[email protected]>
Cc: Jaehoon Chung <[email protected]>
Reviewed-by: Jaehoon Chung <[email protected]>