MIPS: BCM47xx: Fix some WARNINGs pointed in sprom.c by checkpatch.pl

There are still few left:
1) Most of them about lines over 80 chars (increased readability exception)
2) Wrong parsing of preprocessor macros

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/11356/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>