[SPARC]: Linux always started with 9600 8N1

The Linux kernel ignored the PROM's serial settings (115200,n,8,1 in
my case). This was because mode_prop remained "ttyX-mode" (expected:
"ttya-mode") due to the constness of string literals when used with
"char *". Since there is no "ttyX-mode" property in the PROM, Linux
always used the default 9600.

[ Investigation of the suncore.s assembler reveals that gcc optimizied
  away the stores, yet did not emit a warning, which is a pretty
  anti-social thing to do and is the only reason this bug lived for
  so long -DaveM ]

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>