mmc: dw_mmc: make const arrays mszs static

Don't populate the const arrays mszs on the stack, instead make them
static. Makes the object code smaller by over 310 bytes:

Before:
   text	   data	    bss	    dec	    hex	filename
  47527	   8528	    320	  56375	   dc37	drivers/mmc/host/dw_mmc.o

After:
   text	   data	    bss	    dec	    hex	filename
  47055	   8688	    320	  56063	   daff	drivers/mmc/host/dw_mmc.o

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>