wimax/i2400m: don't write to memory allocated by request_firmware()

In kernel 2.6.31, the firmware requested to ram could be marked
with read only attribute, and we can't write any thing directly
to the memory when setting up the last JUMP brh cmd.

Changed so that the scratch buffer is used.

Signed-off-by: Cindy H Kao <cindy.h.kao@intel.com>
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>