serial: Fix sparc driver name strings.

They were all "serial" so if multiple of these drivers registered,
we'd trigger sysfs directory creation errors:

[    1.695793] proc_dir_entry 'serial' already registered
[    1.695839] Call Trace:
[    1.831891]  [00000000004f2534] create_proc_entry+0x7c/0x98
[    1.833608]  [00000000004f3a58] proc_tty_register_driver+0x40/0x70
[    1.833663]  [0000000000594700] tty_register_driver+0x1fc/0x208
[    1.835371]  [00000000005aade4] uart_register_driver+0x134/0x16c
[    1.841762]  [00000000005ac274] sunserial_register_minors+0x34/0x68
[    1.841818]  [00000000007db2a4] sunsu_init+0xf8/0x150
[    1.867697]  [00000000007c62a4] kernel_init+0x190/0x330
[    1.939147]  [0000000000426cf8] kernel_thread+0x38/0x48
[    1.939198]  [00000000006a0d90] rest_init+0x18/0x5c

Signed-off-by: David S. Miller <davem@davemloft.net>