[patch 2.4] au1x00 prom.c hw addr case insensitivity fix

Hi folks,

Attached please find a short fix to str2hexnum() in
arch/mips/au1000/common/prom.c of the 2.4 branch.  With this fix,
the contents of the "ethaddr" entry in the environment table passed
by the bootloader to the kernel can have upper case hexadecimal
digits.  

Without the patch, an address such as ethaddr =
"00:50:C2:0C:20:4f" is silently converted to "00:50:02:00:20:4f",
making for some serious head scratching if you're trying to bootp
the kernel.

Dan