b43: do not use SSB specific flags when calling core reset function

Luckily the only flag we use when calling core reset is GMODE one.
Thanks to that we can just switch to single bool and make function calls
bus generic.

Tested on my BCM4312 (LP-PHY) and early tested with BCM43224.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>