ssb: fix init regression of hostmode PCI core

Our workarounds seem to be clientmode PCI specific. Using SPROM
workaround on SoC resulted in Oops:

Data bus error, epc == 8017ed58, ra == 80225838
 Oops[#1]:
 Cpu 0
 $ 0   : 00000000 10008000 b8000000 00000001
 $ 4   : 80293b5c 00000caa ffffffff 00000000
 $ 8   : 0000000a 00000003 00000001 696d6d20
 $12   : ffffffff 00000000 00000000 ffffffff
 $16   : 802d0140 b8004800 802c0000 00000000
 $20   : 00000000 802c0000 00000000 802d04d4
 $24   : 00000018 80151a00
 $28   : 81816000 81817df8 8029bda0 80225838
 Hi    : 00000000
 Lo    : 00000000
 epc   : 8017ed58 ssb_ssb_read16+0x48/0x60
   Not tainted
 ra    : 80225838 ssb_pcicore_init+0x54/0x3b4

Reported-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Tested-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>