i2c: designware_i2c: remove apparently redundant read of 'i2c, speeds' DT property

This code first figures out if there is an i2c,speeds property, if so
its size in u32s, and then reads the value into the local speeds[]
array. Both 'size' and 'speeds' are completely unused thereafter.

It's not at all clear what this is supposed to do. Of course, it could
be seen as a sanity check that the DT node does have an i2c,speeds
property with an appropriate number of elements, but for that one
wouldn't actually need to read it into speeds[]. Also, I can't find
anywhere else in the U-Boot code which makes use of values from that
property (this is is the only C code referencing "i2c,speeds"), so it
seems pointless to insist that it's there.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>