brcmsmac: make function wlc_phy_workarounds_nphy_rev1 static

The function wlc_phy_workarounds_nphy_rev1 is local to the source and
does not need to be in global scope, so make it static.

Cleans up sparse warning:
symbol 'wlc_phy_workarounds_nphy_rev1' was not declared. Should it
be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>