brcmsmac: remove si_pmu_spuravoid_pllupdate()

si_pmu_spuravoid_pllupdate() is now replaced by
bcma_pmu_spuravoid_pllupdate() which does the same thing, but supports
more chips.

This function is in my pending patch series for bcma.
Author: Hauke Mehrtens <hauke@hauke-m.de>
Date:   Mon Jun 4 01:31:32 2012 +0200

    bcma: add bcma_pmu_spuravoid_pllupdate()

Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>